Definition 8

The duality scalar product of a multiform Φ normal-Φ \Phi roman_Φ with a multivector X 𝑋 X italic_X is the scalar Φ , X normal-Φ 𝑋 \left\langle\Phi,X\right\rangle ⟨ roman_Φ , italic_X ⟩ defined by the following axioms:

For all α , β : normal-: 𝛼 𝛽 absent \alpha,\beta\in\mathbb{R}: italic_α , italic_β ∈ blackboard_R :

α , β = β , α = α β . 𝛼 𝛽 𝛽 𝛼 𝛼 𝛽 \left\langle\alpha,\beta\right\rangle=\left\langle\beta,\alpha\right\rangle=% \alpha\beta. ⟨ italic_α , italic_β ⟩ = ⟨ italic_β , italic_α ⟩ = italic_α italic_β . (9)

For all Φ p p V subscript normal-Φ 𝑝 superscript 𝑝 superscript 𝑉 normal-∗ \Phi_{p}\in{\textstyle\bigwedge\nolimits^{p}}V^{\ast} roman_Φ start_POSTSUBSCRIPT italic_p end_POSTSUBSCRIPT ∈ ⋀ start_POSTSUPERSCRIPT italic_p end_POSTSUPERSCRIPT italic_V start_POSTSUPERSCRIPT ∗ end_POSTSUPERSCRIPT and X p p V superscript 𝑋 𝑝 superscript 𝑝 𝑉 X^{p}\in{\textstyle\bigwedge\nolimits^{p}}V italic_X start_POSTSUPERSCRIPT italic_p end_POSTSUPERSCRIPT ∈ ⋀ start_POSTSUPERSCRIPT italic_p end_POSTSUPERSCRIPT italic_V (with 1 p n 1 𝑝 𝑛 1\leq p\leq n 1 ≤ italic_p ≤ italic_n ) : normal-: : :

Φ p , X p = X p , Φ p = 1 p ! Φ p ( e j 1 , , e j p ) X p ( ε j 1 , , ε j p ) , subscript Φ 𝑝 superscript 𝑋 𝑝 superscript 𝑋 𝑝 subscript Φ 𝑝 1 𝑝 subscript Φ 𝑝 subscript 𝑒 subscript 𝑗 1 subscript 𝑒 subscript 𝑗 𝑝 superscript 𝑋 𝑝 superscript 𝜀 subscript 𝑗 1 superscript 𝜀 subscript 𝑗 𝑝 \left\langle\Phi_{p},X^{p}\right\rangle=\left\langle X^{p},\Phi_{p}\right% \rangle=\frac{1}{p!}\Phi_{p}(e_{j_{1}},\ldots,e_{j_{p}})X^{p}(\varepsilon^{j_{% 1}},\ldots,\varepsilon^{j_{p}}), ⟨ roman_Φ start_POSTSUBSCRIPT italic_p end_POSTSUBSCRIPT , italic_X start_POSTSUPERSCRIPT italic_p end_POSTSUPERSCRIPT ⟩ = ⟨ italic_X start_POSTSUPERSCRIPT italic_p end_POSTSUPERSCRIPT , roman_Φ start_POSTSUBSCRIPT italic_p end_POSTSUBSCRIPT ⟩ = divide start_ARG 1 end_ARG start_ARG italic_p ! end_ARG roman_Φ start_POSTSUBSCRIPT italic_p end_POSTSUBSCRIPT ( italic_e start_POSTSUBSCRIPT italic_j start_POSTSUBSCRIPT 1 end_POSTSUBSCRIPT end_POSTSUBSCRIPT , … , italic_e start_POSTSUBSCRIPT italic_j start_POSTSUBSCRIPT italic_p end_POSTSUBSCRIPT end_POSTSUBSCRIPT ) italic_X start_POSTSUPERSCRIPT italic_p end_POSTSUPERSCRIPT ( italic_ε start_POSTSUPERSCRIPT italic_j start_POSTSUBSCRIPT 1 end_POSTSUBSCRIPT end_POSTSUPERSCRIPT , … , italic_ε start_POSTSUPERSCRIPT italic_j start_POSTSUBSCRIPT italic_p end_POSTSUBSCRIPT end_POSTSUPERSCRIPT ) , (10)

where { e j , ε j } subscript 𝑒 𝑗 superscript 𝜀 𝑗 \left\{e_{j},\varepsilon^{j}\right\} { italic_e start_POSTSUBSCRIPT italic_j end_POSTSUBSCRIPT , italic_ε start_POSTSUPERSCRIPT italic_j end_POSTSUPERSCRIPT } is any pair of dual bases over V . 𝑉 V. italic_V .

For all Φ V normal-Φ superscript 𝑉 normal-∗ \Phi\in{\textstyle\bigwedge}V^{\ast} roman_Φ ∈ ⋀ italic_V start_POSTSUPERSCRIPT ∗ end_POSTSUPERSCRIPT and X V : normal-: 𝑋 𝑉 absent X\in{\textstyle\bigwedge}V: italic_X ∈ ⋀ italic_V : if Φ = Φ 0 + Φ 1 + + Φ n normal-Φ subscript normal-Φ 0 subscript normal-Φ 1 normal-⋯ subscript normal-Φ 𝑛 \Phi=\Phi_{0}+\Phi_{1}+\cdots+\Phi_{n} roman_Φ = roman_Φ start_POSTSUBSCRIPT 0 end_POSTSUBSCRIPT + roman_Φ start_POSTSUBSCRIPT 1 end_POSTSUBSCRIPT + ⋯ + roman_Φ start_POSTSUBSCRIPT italic_n end_POSTSUBSCRIPT and X = X 0 + X 1 + + X n , 𝑋 superscript 𝑋 0 superscript 𝑋 1 normal-⋯ superscript 𝑋 𝑛 X=X^{0}+X^{1}+\cdots+X^{n}, italic_X = italic_X start_POSTSUPERSCRIPT 0 end_POSTSUPERSCRIPT + italic_X start_POSTSUPERSCRIPT 1 end_POSTSUPERSCRIPT + ⋯ + italic_X start_POSTSUPERSCRIPT italic_n end_POSTSUPERSCRIPT , then

Φ , X = X , Φ = p = 0 𝑛 Φ p , X p . Φ 𝑋 𝑋 Φ 𝑛 𝑝 0 subscript Φ 𝑝 superscript 𝑋 𝑝 \left\langle\Phi,X\right\rangle=\left\langle X,\Phi\right\rangle=\overset{n}{% \underset{p=0}{{\textstyle\sum}}}\left\langle\Phi_{p},X^{p}\right\rangle. ⟨ roman_Φ , italic_X ⟩ = ⟨ italic_X , roman_Φ ⟩ = italic_n start_ARG start_UNDERACCENT italic_p = 0 end_UNDERACCENT start_ARG ∑ end_ARG end_ARG ⟨ roman_Φ start_POSTSUBSCRIPT italic_p end_POSTSUBSCRIPT , italic_X start_POSTSUPERSCRIPT italic_p end_POSTSUPERSCRIPT ⟩ . (11)

Definition 10 .

The intensity functional of a (ST)CFMPP Ψ normal-Ψ \Psi roman_Ψ is given by

λ ( g , l , f ) = ρ ( 1 ) ( g , l , f ) . 𝜆 𝑔 𝑙 𝑓 superscript 𝜌 1 𝑔 𝑙 𝑓 \lambda(g,l,f)=\rho^{(1)}(g,l,f). italic_λ ( italic_g , italic_l , italic_f ) = italic_ρ start_POSTSUPERSCRIPT ( 1 ) end_POSTSUPERSCRIPT ( italic_g , italic_l , italic_f ) .

Definition 3.1 .

Let G 𝐺 G italic_G and H 𝐻 H italic_H be finite groups. A (free) ( G , H ) 𝐺 𝐻 (G,H) ( italic_G , italic_H ) -biset Ω Ω \Omega roman_Ω is a set endowed with a free left H 𝐻 H italic_H -action and a free right G 𝐺 G italic_G -action, which commute:

h ( ω g ) = ( h ω ) g 𝜔 𝑔 𝜔 𝑔 h\cdot(\omega\cdot g)=(h\cdot\omega)\cdot g italic_h ⋅ ( italic_ω ⋅ italic_g ) = ( italic_h ⋅ italic_ω ) ⋅ italic_g

When it is not clear from context which groups act on Ω Ω \Omega roman_Ω , we write Ω G H subscript subscript Ω 𝐺 𝐻 {}_{H}\Omega_{G} start_FLOATSUBSCRIPT italic_H end_FLOATSUBSCRIPT roman_Ω start_POSTSUBSCRIPT italic_G end_POSTSUBSCRIPT .

Equivalently, Ω Ω \Omega roman_Ω is a left ( H × G ) 𝐻 𝐺 (H\times G) ( italic_H × italic_G ) -set such that the restrictions of the action to H × 1 𝐻 1 H\times 1 italic_H × 1 and 1 × G 1 𝐺 1\times G 1 × italic_G are free. This equivalence is formed by setting

( h , g ) ω = h ω g - 1 . 𝑔 𝜔 𝜔 superscript 𝑔 1 (h,g)\cdot\omega=h\cdot\omega\cdot g^{-1}. ( italic_h , italic_g ) ⋅ italic_ω = italic_h ⋅ italic_ω ⋅ italic_g start_POSTSUPERSCRIPT - 1 end_POSTSUPERSCRIPT .

Given a ( G , H ) 𝐺 𝐻 (G,H) ( italic_G , italic_H ) -biset Ω Ω \Omega roman_Ω the opposite biset is the ( H , G ) 𝐻 𝐺 (H,G) ( italic_H , italic_G ) -biset Ω o superscript Ω o \Omega^{\mathrm{o}} roman_Ω start_POSTSUPERSCRIPT roman_o end_POSTSUPERSCRIPT with the same underlying set and with action defined by

g ω o h := h - 1 ω g - 1 . assign 𝑔 superscript 𝜔 o superscript 1 𝜔 superscript 𝑔 1 g\cdot\omega^{\mathrm{o}}\cdot h:=h^{-1}\cdot\omega\cdot g^{-1}. italic_g ⋅ italic_ω start_POSTSUPERSCRIPT roman_o end_POSTSUPERSCRIPT ⋅ italic_h := italic_h start_POSTSUPERSCRIPT - 1 end_POSTSUPERSCRIPT ⋅ italic_ω ⋅ italic_g start_POSTSUPERSCRIPT - 1 end_POSTSUPERSCRIPT .

If G = H 𝐺 𝐻 G=H italic_G = italic_H and Ω Ω o Ω superscript Ω o \Omega\cong\Omega^{\mathrm{o}} roman_Ω ≅ roman_Ω start_POSTSUPERSCRIPT roman_o end_POSTSUPERSCRIPT as ( G , G ) 𝐺 𝐺 (G,G) ( italic_G , italic_G ) -bisets, we say Ω Ω \Omega roman_Ω is symmetric .

Denote by A + ( G , H ) subscript 𝐴 𝐺 𝐻 A_{+}(G,H) italic_A start_POSTSUBSCRIPT + end_POSTSUBSCRIPT ( italic_G , italic_H ) the monoid of isomorphism classes of ( G , H ) 𝐺 𝐻 (G,H) ( italic_G , italic_H ) -bisets with disjoint union as addition. If Ω A + ( G , H ) Ω subscript 𝐴 𝐺 𝐻 \Omega\in A_{+}(G,H) roman_Ω ∈ italic_A start_POSTSUBSCRIPT + end_POSTSUBSCRIPT ( italic_G , italic_H ) and Λ A + ( H , K ) Λ subscript 𝐴 𝐻 𝐾 \Lambda\in A_{+}(H,K) roman_Λ ∈ italic_A start_POSTSUBSCRIPT + end_POSTSUBSCRIPT ( italic_H , italic_K ) , we define the ( G , K ) 𝐺 𝐾 (G,K) ( italic_G , italic_K ) -biset Λ Ω Λ Ω \Lambda\circ\Omega roman_Λ ∘ roman_Ω to be Λ × H Ω subscript 𝐻 Λ Ω \Lambda\times_{H}\Omega roman_Λ × start_POSTSUBSCRIPT italic_H end_POSTSUBSCRIPT roman_Ω . With \circ as composition, the monoids A + ( G , H ) subscript 𝐴 𝐺 𝐻 A_{+}(G,H) italic_A start_POSTSUBSCRIPT + end_POSTSUBSCRIPT ( italic_G , italic_H ) form the morphism sets of a category where the objects are all finite groups. This is also the reason why a ( G , H ) 𝐺 𝐻 (G,H) ( italic_G , italic_H ) -biset has G 𝐺 G italic_G acting from the right and not the left, so that the composition order of bisets Λ Ω Λ Ω \Lambda\circ\Omega roman_Λ ∘ roman_Ω fits with the general convention for maps and morphisms.

The point-stabilizer of an element ω 𝜔 \omega italic_ω in a ( G , H ) 𝐺 𝐻 (G,H) ( italic_G , italic_H ) -biset Ω Ω \Omega roman_Ω is Stab H × G ( ω ) H × G subscript Stab 𝐻 𝐺 𝜔 𝐻 𝐺 \operatorname{Stab}_{H\times G}(\omega)\leq H\times G roman_Stab start_POSTSUBSCRIPT italic_H × italic_G end_POSTSUBSCRIPT ( italic_ω ) ≤ italic_H × italic_G , the subgroup consisting of all pairs ( h , g ) 𝑔 (h,g) ( italic_h , italic_g ) such that h ω = ω g 𝜔 𝜔 𝑔 h\cdot\omega=\omega\cdot g italic_h ⋅ italic_ω = italic_ω ⋅ italic_g , or equivalently h ω g - 1 = ω 𝜔 superscript 𝑔 1 𝜔 h\cdot\omega\cdot g^{-1}=\omega italic_h ⋅ italic_ω ⋅ italic_g start_POSTSUPERSCRIPT - 1 end_POSTSUPERSCRIPT = italic_ω . A (injective) ( G , H ) 𝐺 𝐻 (G,H) ( italic_G , italic_H ) -pair is a pair ( K , φ ) 𝐾 𝜑 (K,\varphi) ( italic_K , italic_φ ) with K G 𝐾 𝐺 K\leq G italic_K ≤ italic_G and φ : K H : 𝜑 𝐾 𝐻 \varphi\colon K\to H italic_φ : italic_K → italic_H an injective group map. If ( K , φ ) 𝐾 𝜑 (K,\varphi) ( italic_K , italic_φ ) is a ( G , H ) 𝐺 𝐻 (G,H) ( italic_G , italic_H ) -pair, denote by [ K , φ ] 𝐾 𝜑 [K,\varphi] [ italic_K , italic_φ ] the ( G , H ) 𝐺 𝐻 (G,H) ( italic_G , italic_H ) -biset H × ( K , φ ) G := H × G / ( h , k g ) ( h φ ( k ) , g ) assign subscript 𝐾 𝜑 𝐻 𝐺 𝐻 𝐺 𝑘 𝑔 similar-to 𝜑 𝑘 𝑔 H\times_{(K,\varphi)}G:=H\times G/(h,kg)\sim(h\varphi(k),g) italic_H × start_POSTSUBSCRIPT ( italic_K , italic_φ ) end_POSTSUBSCRIPT italic_G := italic_H × italic_G / ( italic_h , italic_k italic_g ) ∼ ( italic_h italic_φ ( italic_k ) , italic_g ) . If we also denote by ( K , φ ) 𝐾 𝜑 (K,\varphi) ( italic_K , italic_φ ) the graph of φ : K H : 𝜑 𝐾 𝐻 \varphi\colon K\to H italic_φ : italic_K → italic_H :

( K , φ ) := { ( φ ( k ) , k ) H × G } , fragments fragments ( K , φ ) assign fragments { fragments ( φ fragments ( k ) , k ) H G } , (K,\varphi):=\left\{(\varphi(k),k)\in H\times G\right\}, ( italic_K , italic_φ ) := { ( italic_φ ( italic_k ) , italic_k ) ∈ italic_H × italic_G } ,

then [ K , φ ] ( H × G ) / ( K , φ ) 𝐾 𝜑 𝐻 𝐺 𝐾 𝜑 [K,\varphi]\cong(H\times G)/(K,\varphi) [ italic_K , italic_φ ] ≅ ( italic_H × italic_G ) / ( italic_K , italic_φ ) as H × G 𝐻 𝐺 H\times G italic_H × italic_G -sets.

We will also refer to the graph ( K , φ ) 𝐾 𝜑 (K,\varphi) ( italic_K , italic_φ ) as a twisted diagonal (subgroup) . In the case that G = H = S 𝐺 𝐻 𝑆 G=H=S italic_G = italic_H = italic_S is a finite p 𝑝 p italic_p -group, K = P S 𝐾 𝑃 𝑆 K=P\leq S italic_K = italic_P ≤ italic_S , and φ ( P , S ) 𝜑 𝑃 𝑆 \varphi\in\mathcal{F}(P,S) italic_φ ∈ caligraphic_F ( italic_P , italic_S ) for a given fusion system \mathcal{F} caligraphic_F on S 𝑆 S italic_S , we will refer to ( P , φ ) 𝑃 𝜑 (P,\varphi) ( italic_P , italic_φ ) as an \mathcal{F} caligraphic_F -twisted diagonal (subgroup) .

The ( G , H ) 𝐺 𝐻 (G,H) ( italic_G , italic_H ) -pairs ( K , φ ) 𝐾 𝜑 (K,\varphi) ( italic_K , italic_φ ) and ( L , ψ ) 𝐿 𝜓 (L,\psi) ( italic_L , italic_ψ ) are ( G , H ) 𝐺 𝐻 (G,H) ( italic_G , italic_H ) -conjugate if there are elements g N G ( K , L ) 𝑔 subscript 𝑁 𝐺 𝐾 𝐿 g\in N_{G}(K,L) italic_g ∈ italic_N start_POSTSUBSCRIPT italic_G end_POSTSUBSCRIPT ( italic_K , italic_L ) and h N H ( φ ( K ) , ψ ( L ) ) subscript 𝑁 𝐻 𝜑 𝐾 𝜓 𝐿 h\in N_{H}(\varphi(K),\psi(L)) italic_h ∈ italic_N start_POSTSUBSCRIPT italic_H end_POSTSUBSCRIPT ( italic_φ ( italic_K ) , italic_ψ ( italic_L ) ) such that L = K g 𝐿 superscript 𝐾 𝑔 L=\prescript{g\!}{}{}K italic_L = start_FLOATSUPERSCRIPT italic_g end_FLOATSUPERSCRIPT italic_K and

\xymatrix K \ar [ r ] φ \ar [ d ] c g & H \ar [ d ] c h L \ar [ r ] ψ & H \xymatrix 𝐾 \ar superscript delimited-[] 𝑟 𝜑 \ar subscript delimited-[] 𝑑 subscript 𝑐 𝑔 & 𝐻 \ar superscript delimited-[] 𝑑 subscript 𝑐 𝐿 \ar subscript delimited-[] 𝑟 𝜓 & 𝐻 \xymatrix{K\ar[r]^{\varphi}\ar[d]_{c_{g}}&H\ar[d]^{c_{h}}\\ L\ar[r]_{\psi}&H} italic_K [ italic_r ] start_POSTSUPERSCRIPT italic_φ end_POSTSUPERSCRIPT [ italic_d ] start_POSTSUBSCRIPT italic_c start_POSTSUBSCRIPT italic_g end_POSTSUBSCRIPT end_POSTSUBSCRIPT & italic_H [ italic_d ] start_POSTSUPERSCRIPT italic_c start_POSTSUBSCRIPT italic_h end_POSTSUBSCRIPT end_POSTSUPERSCRIPT italic_L [ italic_r ] start_POSTSUBSCRIPT italic_ψ end_POSTSUBSCRIPT & italic_H

commutes. This happens if and only if the twisted diagonals ( K , φ ) 𝐾 𝜑 (K,\varphi) ( italic_K , italic_φ ) and ( L , ψ ) 𝐿 𝜓 (L,\psi) ( italic_L , italic_ψ ) are conjugate as subgroups of H × G 𝐻 𝐺 H\times G italic_H × italic_G .


Definition 2.9 (Skew-rotation) .

We shall refer to the matrix

τ = ( 0 - 1 1 0 1 0 ) . 𝜏 0 1 1 0 missing-subexpression missing-subexpression missing-subexpression missing-subexpression 1 0 \tau=\left(\begin{array}[]{cccc}0&\cdots&\cdots&-1\\ 1&0&&\vdots\\ &\ddots&\ddots&\vdots\\ &&1&0\end{array}\right). italic_τ = ( start_ARRAY start_ROW start_CELL 0 end_CELL start_CELL ⋯ end_CELL start_CELL ⋯ end_CELL start_CELL - 1 end_CELL end_ROW start_ROW start_CELL 1 end_CELL start_CELL 0 end_CELL start_CELL end_CELL start_CELL ⋮ end_CELL end_ROW start_ROW start_CELL end_CELL start_CELL ⋱ end_CELL start_CELL ⋱ end_CELL start_CELL ⋮ end_CELL end_ROW start_ROW start_CELL end_CELL start_CELL end_CELL start_CELL 1 end_CELL start_CELL 0 end_CELL end_ROW end_ARRAY ) .

as a skew-rotation .


Definition 3.6 .

The combinatorial connection α 𝛼 \mathrm{\alpha} italic_α is flat if its curvature is zero for each pair ( σ L ( η ) , η ) 𝜎 𝐿 𝜂 𝜂 (\sigma\in L(\eta),\eta) ( italic_σ ∈ italic_L ( italic_η ) , italic_η ) , i.e. if

α ( η , τ + ) α ( τ + , σ ) = α ( η , τ - ) α ( τ - , σ ) 𝛼 𝜂 superscript 𝜏 𝛼 superscript 𝜏 𝜎 𝛼 𝜂 superscript 𝜏 𝛼 superscript 𝜏 𝜎 \mathrm{\alpha}(\eta,\tau^{+})\mathrm{\alpha}(\tau^{+},\sigma)=\mathrm{\alpha}% (\eta,\tau^{-})\mathrm{\alpha}(\tau^{-},\sigma) italic_α ( italic_η , italic_τ start_POSTSUPERSCRIPT + end_POSTSUPERSCRIPT ) italic_α ( italic_τ start_POSTSUPERSCRIPT + end_POSTSUPERSCRIPT , italic_σ ) = italic_α ( italic_η , italic_τ start_POSTSUPERSCRIPT - end_POSTSUPERSCRIPT ) italic_α ( italic_τ start_POSTSUPERSCRIPT - end_POSTSUPERSCRIPT , italic_σ )

for each such pair ( σ , η ) 𝜎 𝜂 (\sigma,\eta) ( italic_σ , italic_η ) .


Definition 1.3

(i) A Hom-associative algebra is a triple ( A , μ , α ) 𝐴 𝜇 𝛼 (A,\mu,\alpha) ( italic_A , italic_μ , italic_α ) , in which A 𝐴 A italic_A is a linear space, α : A A normal-: 𝛼 normal-→ 𝐴 𝐴 \alpha:A\rightarrow A italic_α : italic_A → italic_A and μ : A A A normal-: 𝜇 normal-→ tensor-product 𝐴 𝐴 𝐴 \mu:A\otimes A\rightarrow A italic_μ : italic_A ⊗ italic_A → italic_A are linear maps, with notation μ ( a a ) = a a 𝜇 tensor-product 𝑎 superscript 𝑎 normal-′ 𝑎 superscript 𝑎 normal-′ \mu(a\otimes a^{\prime})=aa^{\prime} italic_μ ( italic_a ⊗ italic_a start_POSTSUPERSCRIPT ′ end_POSTSUPERSCRIPT ) = italic_a italic_a start_POSTSUPERSCRIPT ′ end_POSTSUPERSCRIPT , such that

α ( a a ) = α ( a ) α ( a ) , ( m u l t i p l i c a t i v i t y ) 𝛼 𝑎 superscript 𝑎 𝛼 𝑎 𝛼 superscript 𝑎 𝑚 𝑢 𝑙 𝑡 𝑖 𝑝 𝑙 𝑖 𝑐 𝑎 𝑡 𝑖 𝑣 𝑖 𝑡 𝑦 \displaystyle\alpha(aa^{\prime})=\alpha(a)\alpha(a^{\prime}),\;\;\;\;\;(multiplicativity) italic_α ( italic_a italic_a start_POSTSUPERSCRIPT ′ end_POSTSUPERSCRIPT ) = italic_α ( italic_a ) italic_α ( italic_a start_POSTSUPERSCRIPT ′ end_POSTSUPERSCRIPT ) , ( italic_m italic_u italic_l italic_t italic_i italic_p italic_l italic_i italic_c italic_a italic_t italic_i italic_v italic_i italic_t italic_y )
α ( a ) ( a a ′′ ) = ( a a ) α ( a ′′ ) , ( H o m - a s s o c i a t i v i t y ) 𝛼 𝑎 superscript 𝑎 superscript 𝑎 ′′ 𝑎 superscript 𝑎 𝛼 superscript 𝑎 ′′ 𝐻 𝑜 𝑚 𝑎 𝑠 𝑠 𝑜 𝑐 𝑖 𝑎 𝑡 𝑖 𝑣 𝑖 𝑡 𝑦 \displaystyle\alpha(a)(a^{\prime}a^{\prime\prime})=(aa^{\prime})\alpha(a^{% \prime\prime}),\;\;\;\;\;(Hom-associativity) italic_α ( italic_a ) ( italic_a start_POSTSUPERSCRIPT ′ end_POSTSUPERSCRIPT italic_a start_POSTSUPERSCRIPT ′ ′ end_POSTSUPERSCRIPT ) = ( italic_a italic_a start_POSTSUPERSCRIPT ′ end_POSTSUPERSCRIPT ) italic_α ( italic_a start_POSTSUPERSCRIPT ′ ′ end_POSTSUPERSCRIPT ) , ( italic_H italic_o italic_m - italic_a italic_s italic_s italic_o italic_c italic_i italic_a italic_t italic_i italic_v italic_i italic_t italic_y )

for all a , a , a ′′ A 𝑎 superscript 𝑎 normal-′ superscript 𝑎 normal-′′ 𝐴 a,a^{\prime},a^{\prime\prime}\in A italic_a , italic_a start_POSTSUPERSCRIPT ′ end_POSTSUPERSCRIPT , italic_a start_POSTSUPERSCRIPT ′ ′ end_POSTSUPERSCRIPT ∈ italic_A . We call α 𝛼 \alpha italic_α the structure map of A 𝐴 A italic_A .

A morphism f : ( A , μ A , α A ) ( B , μ B , α B ) normal-: 𝑓 normal-→ 𝐴 subscript 𝜇 𝐴 subscript 𝛼 𝐴 𝐵 subscript 𝜇 𝐵 subscript 𝛼 𝐵 f:(A,\mu_{A},\alpha_{A})\rightarrow(B,\mu_{B},\alpha_{B}) italic_f : ( italic_A , italic_μ start_POSTSUBSCRIPT italic_A end_POSTSUBSCRIPT , italic_α start_POSTSUBSCRIPT italic_A end_POSTSUBSCRIPT ) → ( italic_B , italic_μ start_POSTSUBSCRIPT italic_B end_POSTSUBSCRIPT , italic_α start_POSTSUBSCRIPT italic_B end_POSTSUBSCRIPT ) of Hom-associative algebras is a linear map f : A B normal-: 𝑓 normal-→ 𝐴 𝐵 f:A\rightarrow B italic_f : italic_A → italic_B such that α B f = f α A subscript 𝛼 𝐵 𝑓 𝑓 subscript 𝛼 𝐴 \alpha_{B}\circ f=f\circ\alpha_{A} italic_α start_POSTSUBSCRIPT italic_B end_POSTSUBSCRIPT ∘ italic_f = italic_f ∘ italic_α start_POSTSUBSCRIPT italic_A end_POSTSUBSCRIPT and f μ A = μ B ( f f ) 𝑓 subscript 𝜇 𝐴 subscript 𝜇 𝐵 tensor-product 𝑓 𝑓 f\circ\mu_{A}=\mu_{B}\circ(f\otimes f) italic_f ∘ italic_μ start_POSTSUBSCRIPT italic_A end_POSTSUBSCRIPT = italic_μ start_POSTSUBSCRIPT italic_B end_POSTSUBSCRIPT ∘ ( italic_f ⊗ italic_f ) .
(ii) A Hom-coassociative coalgebra is a triple ( C , Δ , α ) 𝐶 normal-Δ 𝛼 (C,\Delta,\alpha) ( italic_C , roman_Δ , italic_α ) , in which C 𝐶 C italic_C is a linear space, α : C C normal-: 𝛼 normal-→ 𝐶 𝐶 \alpha:C\rightarrow C italic_α : italic_C → italic_C and Δ : C C C normal-: normal-Δ normal-→ 𝐶 tensor-product 𝐶 𝐶 \Delta:C\rightarrow C\otimes C roman_Δ : italic_C → italic_C ⊗ italic_C are linear maps ( α 𝛼 \alpha italic_α is called the structure map of C 𝐶 C italic_C ) such that

( α α ) Δ = Δ α , ( c o m u l t i p l i c a t i v i t y ) tensor-product 𝛼 𝛼 Δ Δ 𝛼 𝑐 𝑜 𝑚 𝑢 𝑙 𝑡 𝑖 𝑝 𝑙 𝑖 𝑐 𝑎 𝑡 𝑖 𝑣 𝑖 𝑡 𝑦 \displaystyle(\alpha\otimes\alpha)\circ\Delta=\Delta\circ\alpha,\;\;\;\;\;(comultiplicativity) ( italic_α ⊗ italic_α ) ∘ roman_Δ = roman_Δ ∘ italic_α , ( italic_c italic_o italic_m italic_u italic_l italic_t italic_i italic_p italic_l italic_i italic_c italic_a italic_t italic_i italic_v italic_i italic_t italic_y )
( Δ α ) Δ = ( α Δ ) Δ . ( H o m - c o a s s o c i a t i v i t y ) fragments fragments ( Δ tensor-product α ) Δ fragments ( α tensor-product Δ ) Δ . italic- fragments ( H o m c o a s s o c i a t i v i t y ) \displaystyle(\Delta\otimes\alpha)\circ\Delta=(\alpha\otimes\Delta)\circ\Delta% .\;\;\;\;\;(Hom-coassociativity) ( roman_Δ ⊗ italic_α ) ∘ roman_Δ = ( italic_α ⊗ roman_Δ ) ∘ roman_Δ . ( italic_H italic_o italic_m - italic_c italic_o italic_a italic_s italic_s italic_o italic_c italic_i italic_a italic_t italic_i italic_v italic_i italic_t italic_y )

A morphism g : ( C , Δ C , α C ) ( D , Δ D , α D ) normal-: 𝑔 normal-→ 𝐶 subscript normal-Δ 𝐶 subscript 𝛼 𝐶 𝐷 subscript normal-Δ 𝐷 subscript 𝛼 𝐷 g:(C,\Delta_{C},\alpha_{C})\rightarrow(D,\Delta_{D},\alpha_{D}) italic_g : ( italic_C , roman_Δ start_POSTSUBSCRIPT italic_C end_POSTSUBSCRIPT , italic_α start_POSTSUBSCRIPT italic_C end_POSTSUBSCRIPT ) → ( italic_D , roman_Δ start_POSTSUBSCRIPT italic_D end_POSTSUBSCRIPT , italic_α start_POSTSUBSCRIPT italic_D end_POSTSUBSCRIPT ) of Hom-coassociative coalgebras is a linear map g : C D normal-: 𝑔 normal-→ 𝐶 𝐷 g:C\rightarrow D italic_g : italic_C → italic_D such that α D g = g α C subscript 𝛼 𝐷 𝑔 𝑔 subscript 𝛼 𝐶 \alpha_{D}\circ g=g\circ\alpha_{C} italic_α start_POSTSUBSCRIPT italic_D end_POSTSUBSCRIPT ∘ italic_g = italic_g ∘ italic_α start_POSTSUBSCRIPT italic_C end_POSTSUBSCRIPT and ( g g ) Δ C = Δ D g tensor-product 𝑔 𝑔 subscript normal-Δ 𝐶 subscript normal-Δ 𝐷 𝑔 (g\otimes g)\circ\Delta_{C}=\Delta_{D}\circ g ( italic_g ⊗ italic_g ) ∘ roman_Δ start_POSTSUBSCRIPT italic_C end_POSTSUBSCRIPT = roman_Δ start_POSTSUBSCRIPT italic_D end_POSTSUBSCRIPT ∘ italic_g .


Definition 2.5 .

For any commuting units a 𝑎 a italic_a and b 𝑏 b italic_b in / 1 superscript 1 \mathcal{L}/\mathcal{L}^{1} caligraphic_L / caligraphic_L start_POSTSUPERSCRIPT 1 end_POSTSUPERSCRIPT , the determinant invariant d ( a , b ) 𝑑 𝑎 𝑏 d(a,b) italic_d ( italic_a , italic_b ) is the nonzero number

d ( a , b ) = det { a , b } . 𝑑 𝑎 𝑏 𝑎 𝑏 d(a,b)=\det\partial\{a,b\}. italic_d ( italic_a , italic_b ) = roman_det ∂ { italic_a , italic_b } .

In particular, d ( a , b ) 𝑑 𝑎 𝑏 d(a,b) italic_d ( italic_a , italic_b ) satisfies the relations in Proposition 2.4 .


Definition 2.1 .

We say that f 𝑓 f italic_f is a semimultiplicative function on P 𝑃 P italic_P if

f ( x ) f ( y ) = f ( x y ) f ( x y ) 𝑓 𝑥 𝑓 𝑦 𝑓 𝑥 𝑦 𝑓 𝑥 𝑦 f(x)f(y)=f(x\land y)f(x\lor y) italic_f ( italic_x ) italic_f ( italic_y ) = italic_f ( italic_x ∧ italic_y ) italic_f ( italic_x ∨ italic_y ) (2.1)

for all x , y P 𝑥 𝑦 𝑃 x,y\in P italic_x , italic_y ∈ italic_P .


Definition 4.2.2 .

Let Y 𝑌 Y italic_Y be a G 𝐺 G italic_G -variety. We construct a closed subscheme Y G subscript 𝑌 𝐺 Y_{G} italic_Y start_POSTSUBSCRIPT italic_G end_POSTSUBSCRIPT of Y / G 𝑌 𝐺 Y/G italic_Y / italic_G as follows. Let φ : Y Y / G : 𝜑 𝑌 𝑌 𝐺 \varphi\colon Y\to Y/G italic_φ : italic_Y → italic_Y / italic_G be the quotient map, and σ 𝜎 \sigma italic_σ the involution of the sheaf of k 𝑘 k italic_k -algebras φ * 𝒪 Y subscript 𝜑 subscript 𝒪 𝑌 \varphi_{*}\mathcal{O}_{Y} italic_φ start_POSTSUBSCRIPT * end_POSTSUBSCRIPT caligraphic_O start_POSTSUBSCRIPT italic_Y end_POSTSUBSCRIPT . We consider the morphism id + σ : φ * 𝒪 Y φ * 𝒪 Y : id 𝜎 subscript 𝜑 subscript 𝒪 𝑌 subscript 𝜑 subscript 𝒪 𝑌 \operatorname{id}+\sigma\colon\varphi_{*}\mathcal{O}_{Y}\to\varphi_{*}\mathcal% {O}_{Y} roman_id + italic_σ : italic_φ start_POSTSUBSCRIPT * end_POSTSUBSCRIPT caligraphic_O start_POSTSUBSCRIPT italic_Y end_POSTSUBSCRIPT → italic_φ start_POSTSUBSCRIPT * end_POSTSUBSCRIPT caligraphic_O start_POSTSUBSCRIPT italic_Y end_POSTSUBSCRIPT of sheaves of k 𝑘 k italic_k -vector spaces on Y / G 𝑌 𝐺 Y/G italic_Y / italic_G . The subsheaf 𝒪 Y / G subscript 𝒪 𝑌 𝐺 \mathcal{O}_{Y/G} caligraphic_O start_POSTSUBSCRIPT italic_Y / italic_G end_POSTSUBSCRIPT of φ * 𝒪 Y subscript 𝜑 subscript 𝒪 𝑌 \varphi_{*}\mathcal{O}_{Y} italic_φ start_POSTSUBSCRIPT * end_POSTSUBSCRIPT caligraphic_O start_POSTSUBSCRIPT italic_Y end_POSTSUBSCRIPT coincides with ker ( id + σ ) kernel id 𝜎 \ker(\operatorname{id}+\sigma) roman_ker ( roman_id + italic_σ ) by [ SGA I , V, Corollaire 1.2] , and ( id + σ ) ( id + σ ) = 0 id 𝜎 id 𝜎 0 (\operatorname{id}+\sigma)\circ(\operatorname{id}+\sigma)=0 ( roman_id + italic_σ ) ∘ ( roman_id + italic_σ ) = 0 . Thus id + σ id 𝜎 \operatorname{id}+\sigma roman_id + italic_σ induces a morphism : φ * 𝒪 Y 𝒪 Y / G : subscript 𝜑 subscript 𝒪 𝑌 subscript 𝒪 𝑌 𝐺 \partial\colon\varphi_{*}\mathcal{O}_{Y}\to\mathcal{O}_{Y/G} ∂ : italic_φ start_POSTSUBSCRIPT * end_POSTSUBSCRIPT caligraphic_O start_POSTSUBSCRIPT italic_Y end_POSTSUBSCRIPT → caligraphic_O start_POSTSUBSCRIPT italic_Y / italic_G end_POSTSUBSCRIPT . If U 𝑈 U italic_U is an open subscheme of Y / G 𝑌 𝐺 Y/G italic_Y / italic_G , and a , b ( φ * 𝒪 Y ) ( U ) 𝑎 𝑏 subscript 𝜑 subscript 𝒪 𝑌 𝑈 a,b\in(\varphi_{*}\mathcal{O}_{Y})(U) italic_a , italic_b ∈ ( italic_φ start_POSTSUBSCRIPT * end_POSTSUBSCRIPT caligraphic_O start_POSTSUBSCRIPT italic_Y end_POSTSUBSCRIPT ) ( italic_U ) , then we have in 𝒪 Y / G ( U ) subscript 𝒪 𝑌 𝐺 𝑈 \mathcal{O}_{Y/G}(U) caligraphic_O start_POSTSUBSCRIPT italic_Y / italic_G end_POSTSUBSCRIPT ( italic_U )

( a b ) = ( a ) ( b ) + a ( b ) + ( a ) b . 𝑎 𝑏 𝑎 𝑏 𝑎 𝑏 𝑎 𝑏 \partial(ab)=\partial(a)\partial(b)+a\partial(b)+\partial(a)b. ∂ ( italic_a italic_b ) = ∂ ( italic_a ) ∂ ( italic_b ) + italic_a ∂ ( italic_b ) + ∂ ( italic_a ) italic_b .

When a 𝒪 Y / G ( U ) ( φ * 𝒪 Y ) ( U ) 𝑎 subscript 𝒪 𝑌 𝐺 𝑈 subscript 𝜑 subscript 𝒪 𝑌 𝑈 a\in\mathcal{O}_{Y/G}(U)\subset(\varphi_{*}\mathcal{O}_{Y})(U) italic_a ∈ caligraphic_O start_POSTSUBSCRIPT italic_Y / italic_G end_POSTSUBSCRIPT ( italic_U ) ⊂ ( italic_φ start_POSTSUBSCRIPT * end_POSTSUBSCRIPT caligraphic_O start_POSTSUBSCRIPT italic_Y end_POSTSUBSCRIPT ) ( italic_U ) , then ( a ) = 0 𝑎 0 \partial(a)=0 ∂ ( italic_a ) = 0 , so that ( a b ) = a ( b ) 𝑎 𝑏 𝑎 𝑏 \partial(ab)=a\partial(b) ∂ ( italic_a italic_b ) = italic_a ∂ ( italic_b ) . This proves that : φ * 𝒪 Y 𝒪 Y / G : subscript 𝜑 subscript 𝒪 𝑌 subscript 𝒪 𝑌 𝐺 \partial\colon\varphi_{*}\mathcal{O}_{Y}\to\mathcal{O}_{Y/G} ∂ : italic_φ start_POSTSUBSCRIPT * end_POSTSUBSCRIPT caligraphic_O start_POSTSUBSCRIPT italic_Y end_POSTSUBSCRIPT → caligraphic_O start_POSTSUBSCRIPT italic_Y / italic_G end_POSTSUBSCRIPT is a morphism of 𝒪 Y / G subscript 𝒪 𝑌 𝐺 \mathcal{O}_{Y/G} caligraphic_O start_POSTSUBSCRIPT italic_Y / italic_G end_POSTSUBSCRIPT -modules. Its image is a quasi-coherent sheaf of ideals of 𝒪 Y / G subscript 𝒪 𝑌 𝐺 \mathcal{O}_{Y/G} caligraphic_O start_POSTSUBSCRIPT italic_Y / italic_G end_POSTSUBSCRIPT , and we define Y G subscript 𝑌 𝐺 Y_{G} italic_Y start_POSTSUBSCRIPT italic_G end_POSTSUBSCRIPT as the corresponding closed subscheme of Y / G 𝑌 𝐺 Y/G italic_Y / italic_G .

Thus when Y = Spec A 𝑌 Spec 𝐴 Y=\operatorname{Spec}A italic_Y = roman_Spec italic_A , the closed subscheme Y G subscript 𝑌 𝐺 Y_{G} italic_Y start_POSTSUBSCRIPT italic_G end_POSTSUBSCRIPT is defined by the ideal im A im subscript 𝐴 \operatorname{im}\partial_{A} roman_im ∂ start_POSTSUBSCRIPT italic_A end_POSTSUBSCRIPT of A G superscript 𝐴 𝐺 A^{G} italic_A start_POSTSUPERSCRIPT italic_G end_POSTSUPERSCRIPT ( Notation 4.1.1 ).


Definition 3 .

Let X 𝑋 X italic_X be a set together with a binary operation denoted ( x , y ) x y maps-to 𝑥 𝑦 subgroup-of 𝑥 𝑦 (x,y)\mapsto x\lhd y ( italic_x , italic_y ) ↦ italic_x ⊲ italic_y such that for all y X 𝑦 𝑋 y\in X italic_y ∈ italic_X , the map x x y maps-to 𝑥 subgroup-of 𝑥 𝑦 x\mapsto x\lhd y italic_x ↦ italic_x ⊲ italic_y is bijective and for all x , y , z X 𝑥 𝑦 𝑧 𝑋 x,y,z\in X italic_x , italic_y , italic_z ∈ italic_X ,

( x y ) z = ( x z ) ( y z ) . subgroup-of subgroup-of 𝑥 𝑦 𝑧 subgroup-of subgroup-of 𝑥 𝑧 subgroup-of 𝑦 𝑧 (x\lhd y)\lhd z\,=\,(x\lhd z)\lhd(y\lhd z). ( italic_x ⊲ italic_y ) ⊲ italic_z = ( italic_x ⊲ italic_z ) ⊲ ( italic_y ⊲ italic_z ) .

Then we call X 𝑋 X italic_X a (right) rack . In case the invertibility of the maps x x y maps-to 𝑥 subgroup-of 𝑥 𝑦 x\mapsto x\lhd y italic_x ↦ italic_x ⊲ italic_y is not required, it is called a shelf .

Definition 4 .

Let G 𝐺 G italic_G be a group and X 𝑋 X italic_X be a (right) G 𝐺 G italic_G -set. Then a map p : X G : 𝑝 𝑋 𝐺 p:X\to G italic_p : italic_X → italic_G is called an augmented rack in case p 𝑝 p italic_p satisfies the augmentation identity, i.e. for all g G 𝑔 𝐺 g\in G italic_g ∈ italic_G and all x X 𝑥 𝑋 x\in X italic_x ∈ italic_X

(1) p ( x g ) = g - 1 p ( x ) g . 𝑝 𝑥 𝑔 superscript 𝑔 1 𝑝 𝑥 𝑔 p(x\cdot g)\,=\,g^{-1}\,p(x)\,g. italic_p ( italic_x ⋅ italic_g ) = italic_g start_POSTSUPERSCRIPT - 1 end_POSTSUPERSCRIPT italic_p ( italic_x ) italic_g .

Definition 1.2 .

Let 0 < b < 1 0 𝑏 1 0<b<1 0 < italic_b < 1 . A probability distribution μ 𝜇 \mu italic_μ on d superscript 𝑑 \mathbb{R}^{d} blackboard_R start_POSTSUPERSCRIPT italic_d end_POSTSUPERSCRIPT is said to be b 𝑏 b italic_b -decomposable if there exists a probability distribution ρ 𝜌 \rho italic_ρ on d superscript 𝑑 \mathbb{R}^{d} blackboard_R start_POSTSUPERSCRIPT italic_d end_POSTSUPERSCRIPT such that

(1.1) μ ^ ( z ) = μ ^ ( b z ) ρ ^ ( z ) . ^ 𝜇 𝑧 ^ 𝜇 𝑏 𝑧 ^ 𝜌 𝑧 \widehat{\mu}(z)=\widehat{\mu}(bz)\widehat{\rho}(z). ^ start_ARG italic_μ end_ARG ( italic_z ) = ^ start_ARG italic_μ end_ARG ( italic_b italic_z ) ^ start_ARG italic_ρ end_ARG ( italic_z ) .

Definition 1.10 .

[ 4 ] A bimodule of Leibniz algebra L 𝐿 L italic_L is a vector space M 𝑀 M italic_M over 𝔽 𝔽 \mathbb{F} blackboard_F equipped with two bilinear compositions denoted by m a 𝑚 𝑎 ma italic_m italic_a and a m , 𝑎 𝑚 am, italic_a italic_m , for any a L 𝑎 𝐿 a\in L italic_a ∈ italic_L and m M , 𝑚 𝑀 m\in M, italic_m ∈ italic_M , satisfy

( m a ) b = m [ a , b ] - a ( m b ) , 𝑚 𝑎 𝑏 𝑚 𝑎 𝑏 𝑎 𝑚 𝑏 (ma)b=m[a,b]-a(mb), ( italic_m italic_a ) italic_b = italic_m [ italic_a , italic_b ] - italic_a ( italic_m italic_b ) ,
( a m ) b = a ( m b ) - m [ a , b ] , 𝑎 𝑚 𝑏 𝑎 𝑚 𝑏 𝑚 𝑎 𝑏 (am)b=a(mb)-m[a,b], ( italic_a italic_m ) italic_b = italic_a ( italic_m italic_b ) - italic_m [ italic_a , italic_b ] ,
[ a , b ] m = a ( b m ) - b ( a m ) . 𝑎 𝑏 𝑚 𝑎 𝑏 𝑚 𝑏 𝑎 𝑚 [a,b]m=a(bm)-b(am). [ italic_a , italic_b ] italic_m = italic_a ( italic_b italic_m ) - italic_b ( italic_a italic_m ) .

Definition 2.25 .

A 2-cocycle on a LCH groupoid 𝒢 𝒢 \mathcal{G} caligraphic_G is a continuous function ω : 𝒢 ( 2 ) 𝕋 : 𝜔 superscript 𝒢 2 𝕋 \omega:\mathcal{G}^{(2)}\to\mathbb{T} italic_ω : caligraphic_G start_POSTSUPERSCRIPT ( 2 ) end_POSTSUPERSCRIPT → blackboard_T such that whenever ( a , b ) , ( b , d ) 𝒢 ( 2 ) 𝑎 𝑏 𝑏 𝑑 superscript 𝒢 2 (a,b),(b,d)\in\mathcal{G}^{(2)} ( italic_a , italic_b ) , ( italic_b , italic_d ) ∈ caligraphic_G start_POSTSUPERSCRIPT ( 2 ) end_POSTSUPERSCRIPT , we have

ω ( a , b d ) ω ( b , d ) = ω ( a b , d ) ω ( a , b ) , 𝜔 𝑎 𝑏 𝑑 𝜔 𝑏 𝑑 𝜔 𝑎 𝑏 𝑑 𝜔 𝑎 𝑏 \omega(a,bd)\omega(b,d)=\omega(ab,d)\omega(a,b), italic_ω ( italic_a , italic_b italic_d ) italic_ω ( italic_b , italic_d ) = italic_ω ( italic_a italic_b , italic_d ) italic_ω ( italic_a , italic_b ) , (6)

and for any a 𝒢 𝑎 𝒢 a\in\mathcal{G} italic_a ∈ caligraphic_G we have

ω ( r ( a ) , a ) = ω ( a , s ( a ) ) = 1 . 𝜔 𝑟 𝑎 𝑎 𝜔 𝑎 𝑠 𝑎 1 \omega(r(a),a)=\omega(a,s(a))=1. italic_ω ( italic_r ( italic_a ) , italic_a ) = italic_ω ( italic_a , italic_s ( italic_a ) ) = 1 . (7)

We write Z 2 ( 𝒢 , 𝕋 ) superscript 𝑍 2 𝒢 𝕋 Z^{2}(\mathcal{G},\mathbb{T}) italic_Z start_POSTSUPERSCRIPT 2 end_POSTSUPERSCRIPT ( caligraphic_G , blackboard_T ) for the set of 2-cocycles on 𝒢 𝒢 \mathcal{G} caligraphic_G .


Definition 3.1

A ternary 𝕂 𝕂 \mathbb{K} blackboard_K -algebra is a triple ( A , μ , η ) 𝐴 𝜇 𝜂 (A,\mu,\eta) ( italic_A , italic_μ , italic_η ) where A 𝐴 A italic_A is a vector space over a field 𝕂 𝕂 \mathbb{K} blackboard_K with a multiplication μ : A A A A : 𝜇 tensor-product 𝐴 𝐴 𝐴 𝐴 \mu:A\otimes A\otimes A\rightarrow A italic_μ : italic_A ⊗ italic_A ⊗ italic_A → italic_A and a unit η : 𝕂 A : 𝜂 𝕂 𝐴 \eta:\mathbb{K}\rightarrow A italic_η : blackboard_K → italic_A that are linear maps such that the following associativity identity is satisfied

μ ( μ i d i d ) = μ ( i d μ i d ) = μ ( i d i d μ ) 𝜇 tensor-product tensor-product 𝜇 𝑖 𝑑 𝑖 𝑑 𝜇 tensor-product 𝑖 𝑑 𝜇 𝑖 𝑑 𝜇 tensor-product tensor-product 𝑖 𝑑 𝑖 𝑑 𝜇 \mu\circ(\mu\otimes id\otimes id)=\mu\circ(id\otimes\mu\otimes id)=\mu\circ(id% \otimes id\otimes\mu) italic_μ ∘ ( italic_μ ⊗ italic_i italic_d ⊗ italic_i italic_d ) = italic_μ ∘ ( italic_i italic_d ⊗ italic_μ ⊗ italic_i italic_d ) = italic_μ ∘ ( italic_i italic_d ⊗ italic_i italic_d ⊗ italic_μ ) (4)

and the following property of the unit is also satisfied

μ ( η η i d ) = μ ( η i d η ) = μ ( i d η η ) . 𝜇 tensor-product 𝜂 𝜂 𝑖 𝑑 𝜇 tensor-product tensor-product 𝜂 𝑖 𝑑 𝜂 𝜇 tensor-product 𝑖 𝑑 𝜂 𝜂 \mu\circ(\eta\otimes\eta\otimes id)=\mu\circ(\eta\otimes id\otimes\eta)=\mu% \circ(id\otimes\eta\otimes\eta). italic_μ ∘ ( italic_η ⊗ italic_η ⊗ italic_i italic_d ) = italic_μ ∘ ( italic_η ⊗ italic_i italic_d ⊗ italic_η ) = italic_μ ∘ ( italic_i italic_d ⊗ italic_η ⊗ italic_η ) .

The triple ( A , μ , η ) 𝐴 𝜇 𝜂 (A,\mu,\eta) ( italic_A , italic_μ , italic_η ) defines a weak ternary 𝕂 𝕂 \mathbb{K} blackboard_K -algebra if, instead of identity ( 4 ), the following weak associativity identity holds

μ ( μ i d i d ) = μ ( i d i d μ ) 𝜇 tensor-product tensor-product 𝜇 𝑖 𝑑 𝑖 𝑑 𝜇 tensor-product tensor-product 𝑖 𝑑 𝑖 𝑑 𝜇 \mu\circ(\mu\otimes id\otimes id)=\mu\circ(id\otimes id\otimes\mu) italic_μ ∘ ( italic_μ ⊗ italic_i italic_d ⊗ italic_i italic_d ) = italic_μ ∘ ( italic_i italic_d ⊗ italic_i italic_d ⊗ italic_μ ) (5)

Definition 1.1 .

The down-up algebra A ( r + s , - r s ) 𝐴 𝑟 𝑠 𝑟 𝑠 A(r+s,-rs) italic_A ( italic_r + italic_s , - italic_r italic_s ) is defined to be a 𝕂 - limit-from 𝕂 \mathbb{K}- blackboard_K - algebra generated by d , u 𝑑 𝑢 d,u italic_d , italic_u subject the following relations:

d 2 u = ( r + s ) d u d - r s u d 2 ; superscript 𝑑 2 𝑢 𝑟 𝑠 𝑑 𝑢 𝑑 𝑟 𝑠 𝑢 superscript 𝑑 2 \displaystyle d^{2}u=(r+s)dud-rsud^{2}; italic_d start_POSTSUPERSCRIPT 2 end_POSTSUPERSCRIPT italic_u = ( italic_r + italic_s ) italic_d italic_u italic_d - italic_r italic_s italic_u italic_d start_POSTSUPERSCRIPT 2 end_POSTSUPERSCRIPT ;
d u 2 = ( r + s ) u d u - r s u 2 d . 𝑑 superscript 𝑢 2 𝑟 𝑠 𝑢 𝑑 𝑢 𝑟 𝑠 superscript 𝑢 2 𝑑 \displaystyle du^{2}=(r+s)udu-rsu^{2}d. italic_d italic_u start_POSTSUPERSCRIPT 2 end_POSTSUPERSCRIPT = ( italic_r + italic_s ) italic_u italic_d italic_u - italic_r italic_s italic_u start_POSTSUPERSCRIPT 2 end_POSTSUPERSCRIPT italic_d .

Definition 44

Let M = ( P , ( t , h ) , f , g , α ) 𝑀 𝑃 𝑡 𝑓 𝑔 𝛼 M=(P,(t,h),f,g,\alpha) italic_M = ( italic_P , ( italic_t , italic_h ) , italic_f , italic_g , italic_α ) be a Schwarzschild model. We define the corresponding Schwarzschild plane Π M subscript normal-Π 𝑀 \Pi_{M} roman_Π start_POSTSUBSCRIPT italic_M end_POSTSUBSCRIPT to be the pseudo-Riemannian manifold ( P , ζ ) 𝑃 𝜁 (P,\zeta) ( italic_P , italic_ζ ) such that

ζ = - ( f h ) d t d t + ( g h ) d h d h 𝜁 tensor-product 𝑓 𝑑 𝑡 𝑑 𝑡 tensor-product 𝑔 𝑑 𝑑 \zeta=-(f\circ h)dt\otimes dt+(g\circ h)dh\otimes dh italic_ζ = - ( italic_f ∘ italic_h ) italic_d italic_t ⊗ italic_d italic_t + ( italic_g ∘ italic_h ) italic_d italic_h ⊗ italic_d italic_h
Definition 61

A Schwarzschild model M = ( P , ( t , h ) , f , g , α ) 𝑀 𝑃 𝑡 𝑓 𝑔 𝛼 M=(P,(t,h),f,g,\alpha) italic_M = ( italic_P , ( italic_t , italic_h ) , italic_f , italic_g , italic_α ) will be called a unimodular model if and only if the special coordinates ( t , h ) 𝑡 (t,h) ( italic_t , italic_h ) of P 𝑃 P italic_P were chosen such that

f ( h ) g ( h ) [ α ( h ) ] 4 = 1 𝑓 𝑔 superscript delimited-[] 𝛼 4 1 f(h)g(h)\left[\alpha(h)\right]^{4}=1 italic_f ( italic_h ) italic_g ( italic_h ) [ italic_α ( italic_h ) ] start_POSTSUPERSCRIPT 4 end_POSTSUPERSCRIPT = 1

Definition 3 (Concatenation product) .

The concatenation product of two injective words π = a 1 a r 𝜋 subscript 𝑎 1 subscript 𝑎 𝑟 \pi=a_{1}\dots a_{r} italic_π = italic_a start_POSTSUBSCRIPT 1 end_POSTSUBSCRIPT … italic_a start_POSTSUBSCRIPT italic_r end_POSTSUBSCRIPT and π = b 1 b s superscript 𝜋 subscript 𝑏 1 subscript 𝑏 𝑠 \pi^{\prime}=b_{1}\dots b_{s} italic_π start_POSTSUPERSCRIPT ′ end_POSTSUPERSCRIPT = italic_b start_POSTSUBSCRIPT 1 end_POSTSUBSCRIPT … italic_b start_POSTSUBSCRIPT italic_s end_POSTSUBSCRIPT such that c ( π ) c ( π ) = 𝑐 𝜋 𝑐 superscript 𝜋 c(\pi)\cap c(\pi^{\prime})=\emptyset italic_c ( italic_π ) ∩ italic_c ( italic_π start_POSTSUPERSCRIPT ′ end_POSTSUPERSCRIPT ) = ∅ is the word π π = a 1 a r b 1 b s 𝜋 superscript 𝜋 subscript 𝑎 1 subscript 𝑎 𝑟 subscript 𝑏 1 subscript 𝑏 𝑠 \pi\pi^{\prime}=a_{1}\dots a_{r}b_{1}\dots b_{s} italic_π italic_π start_POSTSUPERSCRIPT ′ end_POSTSUPERSCRIPT = italic_a start_POSTSUBSCRIPT 1 end_POSTSUBSCRIPT … italic_a start_POSTSUBSCRIPT italic_r end_POSTSUBSCRIPT italic_b start_POSTSUBSCRIPT 1 end_POSTSUBSCRIPT … italic_b start_POSTSUBSCRIPT italic_s end_POSTSUBSCRIPT . It is extended as the bilinear operator L ( Γ n ) × L ( Γ n ) L ( Γ n ) 𝐿 subscript Γ 𝑛 𝐿 subscript Γ 𝑛 𝐿 subscript Γ 𝑛 L(\Gamma_{n})\times L(\Gamma_{n})\rightarrow L(\Gamma_{n}) italic_L ( roman_Γ start_POSTSUBSCRIPT italic_n end_POSTSUBSCRIPT ) × italic_L ( roman_Γ start_POSTSUBSCRIPT italic_n end_POSTSUBSCRIPT ) → italic_L ( roman_Γ start_POSTSUBSCRIPT italic_n end_POSTSUBSCRIPT ) defined on Dirac functions by

( π , π ) { π π if c ( π ) c ( π ) = , 0 otherwise . fragments fragments ( π , superscript 𝜋 ) maps-to fragments { 𝜋 superscript 𝜋 if 𝑐 𝜋 𝑐 superscript 𝜋 0 otherwise (\pi,\pi^{\prime})\mapsto\left\{\begin{aligned} \displaystyle\pi\pi^{\prime}&% \displaystyle\text{if }c(\pi)\cap c(\pi^{\prime})=\emptyset,\\ \displaystyle 0&\displaystyle\text{otherwise}.\end{aligned}\right. ( italic_π , italic_π start_POSTSUPERSCRIPT ′ end_POSTSUPERSCRIPT ) ↦ { start_ROW start_CELL italic_π italic_π start_POSTSUPERSCRIPT ′ end_POSTSUPERSCRIPT end_CELL start_CELL if italic_c ( italic_π ) ∩ italic_c ( italic_π start_POSTSUPERSCRIPT ′ end_POSTSUPERSCRIPT ) = ∅ , end_CELL end_ROW start_ROW start_CELL 0 end_CELL start_CELL otherwise . end_CELL end_ROW
Definition 6 (Diamond operator) .

For x , y L ( Γ n ) 𝑥 𝑦 𝐿 subscript Γ 𝑛 x,y\in L(\Gamma_{n}) italic_x , italic_y ∈ italic_L ( roman_Γ start_POSTSUBSCRIPT italic_n end_POSTSUBSCRIPT ) , we define

x y = x y - y x . 𝑥 𝑦 𝑥 𝑦 𝑦 𝑥 x\diamond y=xy-yx. italic_x ⋄ italic_y = italic_x italic_y - italic_y italic_x .

Definition 5.1 ( [ 4 , Definition on p. 283] ) .

Let X 𝑋 X italic_X be a topological space. A codimension function is a function d : X 𝑑 𝑋 d\mathpunct{:}X\rightarrow\mathbb{Z} italic_d : italic_X → blackboard_Z such that

d ( x ) = d ( x ) + 1 𝑑 superscript 𝑥 𝑑 𝑥 1 d(x^{\prime})=d(x)+1 italic_d ( italic_x start_POSTSUPERSCRIPT ′ end_POSTSUPERSCRIPT ) = italic_d ( italic_x ) + 1

holds for every specialization x { x } ¯ superscript 𝑥 ¯ 𝑥 x^{\prime}\in\overline{\{x\}} italic_x start_POSTSUPERSCRIPT ′ end_POSTSUPERSCRIPT ∈ ¯ start_ARG { italic_x } end_ARG such that codim ( { x } ¯ , { x } ¯ ) = 1 codim ¯ superscript 𝑥 ¯ 𝑥 1 \operatorname{codim}(\overline{\{x^{\prime}\}},\overline{\{x\}})=1 roman_codim ( ¯ start_ARG { italic_x start_POSTSUPERSCRIPT ′ end_POSTSUPERSCRIPT } end_ARG , ¯ start_ARG { italic_x } end_ARG ) = 1 .


Definition 1.1 .

A set-theoretic solution of YBE (or braided quadratic set ) is a pair ( SS , ρ ) SS 𝜌 (\SS,\rho) ( roman_SS , italic_ρ ) where SS SS \SS roman_SS is a set and ρ 𝜌 \rho italic_ρ is a bijection of SS × SS SS SS \SS\times\SS roman_SS × roman_SS into itself that satisfies

(1.1) ρ 12 ρ 23 ρ 12 = ρ 23 ρ 12 ρ 23 . superscript 𝜌 12 superscript 𝜌 23 superscript 𝜌 12 superscript 𝜌 23 superscript 𝜌 12 superscript 𝜌 23 \rho^{12}\rho^{23}\rho^{12}=\rho^{23}\rho^{12}\rho^{23}. italic_ρ start_POSTSUPERSCRIPT 12 end_POSTSUPERSCRIPT italic_ρ start_POSTSUPERSCRIPT 23 end_POSTSUPERSCRIPT italic_ρ start_POSTSUPERSCRIPT 12 end_POSTSUPERSCRIPT = italic_ρ start_POSTSUPERSCRIPT 23 end_POSTSUPERSCRIPT italic_ρ start_POSTSUPERSCRIPT 12 end_POSTSUPERSCRIPT italic_ρ start_POSTSUPERSCRIPT 23 end_POSTSUPERSCRIPT .

where ρ i j superscript 𝜌 𝑖 𝑗 \rho^{ij} italic_ρ start_POSTSUPERSCRIPT italic_i italic_j end_POSTSUPERSCRIPT is the map of SS 3 superscript SS 3 \SS^{3} roman_SS start_POSTSUPERSCRIPT 3 end_POSTSUPERSCRIPT to itself obtained when ρ 𝜌 \rho italic_ρ acts on the i 𝑖 i italic_i th and j 𝑗 j italic_j th entries.

Definition 1.4 (Rump [ 27 ] ) .

A right-cyclic system , or RC-system , is a pair ( SS , * ) SS (\SS,*) ( roman_SS , * ) where * * * is a binary operation on the set SS SS \SS roman_SS that obeys the right-cyclic law R C 𝑅 𝐶 RC italic_R italic_C

(1.7) ( x * y ) * ( x * z ) = ( y * x ) * ( y * z ) . 𝑥 𝑦 𝑥 𝑧 𝑦 𝑥 𝑦 𝑧 (x*y)*(x*z)=(y*x)*(y*z). ( italic_x * italic_y ) * ( italic_x * italic_z ) = ( italic_y * italic_x ) * ( italic_y * italic_z ) .

An RC-quasigroup is an RC-system whose left-translations are one-to-one, that is, for every s 𝑠 s italic_s in SS SS \SS roman_SS , the map t s * t maps-to 𝑡 𝑠 𝑡 t\mapsto s*t italic_t ↦ italic_s * italic_t is one-to-one. An RC-system is called bijective if the map ( s , t ) ( s * t , t * s ) maps-to 𝑠 𝑡 𝑠 𝑡 𝑡 𝑠 (s,t)\mapsto(s*t,t*s) ( italic_s , italic_t ) ↦ ( italic_s * italic_t , italic_t * italic_s ) is a bijection of SS × SS SS SS \SS\times\SS roman_SS × roman_SS to itself.

Definition 1.7 .

An RLC-system is a triple ( SS , * , * ~ ) SS ~ (\SS,*,\mathbin{\tilde{*}}) ( roman_SS , * , start_BINOP ~ start_ARG * end_ARG end_BINOP ) such that ( SS , * ) SS (\SS,*) ( roman_SS , * ) is an RC-system, * ~ ~ \mathbin{\tilde{*}} start_BINOP ~ start_ARG * end_ARG end_BINOP is a second binary operation on SS SS \SS roman_SS that obeys the left-cyclic law L C 𝐿 𝐶 LC italic_L italic_C

(1.10) ( z * ~ x ) * ~ ( y * ~ x ) = ( z * ~ y ) * ~ ( x * ~ y ) , ~ ~ 𝑧 𝑥 ~ 𝑦 𝑥 ~ ~ 𝑧 𝑦 ~ 𝑥 𝑦 (z\mathbin{\tilde{*}}x)\mathbin{\tilde{*}}(y\mathbin{\tilde{*}}x)=(z\mathbin{% \tilde{*}}y)\mathbin{\tilde{*}}(x\mathbin{\tilde{*}}y), ( italic_z start_BINOP ~ start_ARG * end_ARG end_BINOP italic_x ) start_BINOP ~ start_ARG * end_ARG end_BINOP ( italic_y start_BINOP ~ start_ARG * end_ARG end_BINOP italic_x ) = ( italic_z start_BINOP ~ start_ARG * end_ARG end_BINOP italic_y ) start_BINOP ~ start_ARG * end_ARG end_BINOP ( italic_x start_BINOP ~ start_ARG * end_ARG end_BINOP italic_y ) ,

and both operations are connected by

(1.11) ( y * x ) * ~ ( x * y ) = x = ( y * ~ x ) * ( x * ~ y ) . ~ 𝑦 𝑥 𝑥 𝑦 𝑥 ~ 𝑦 𝑥 ~ 𝑥 𝑦 (y*x)\mathbin{\tilde{*}}(x*y)=x=(y\mathbin{\tilde{*}}x)*(x\mathbin{\tilde{*}}y). ( italic_y * italic_x ) start_BINOP ~ start_ARG * end_ARG end_BINOP ( italic_x * italic_y ) = italic_x = ( italic_y start_BINOP ~ start_ARG * end_ARG end_BINOP italic_x ) * ( italic_x start_BINOP ~ start_ARG * end_ARG end_BINOP italic_y ) .

An RLC-quasigroup is an RLC-system ( SS , * , * ~ ) SS ~ (\SS,*,\mathbin{\tilde{*}}) ( roman_SS , * , start_BINOP ~ start_ARG * end_ARG end_BINOP ) such that the left-translations of * * * and the right-translations of * ~ ~ \mathbin{\tilde{*}} start_BINOP ~ start_ARG * end_ARG end_BINOP are one-to-one.


Definition 3.5 .

Let f 𝑓 f italic_f be C 1 superscript 𝐶 1 C^{1} italic_C start_POSTSUPERSCRIPT 1 end_POSTSUPERSCRIPT with respect to x 𝑥 x italic_x , f x 𝑓 𝑥 \frac{\partial f}{\partial x} divide start_ARG ∂ italic_f end_ARG start_ARG ∂ italic_x end_ARG and f 𝑓 f italic_f be continuous with respect to t 𝑡 t italic_t . We will say that W × n 𝑊 superscript 𝑛 W\subset{\mathbb{R}}\times\mathbb{R}^{n} italic_W ⊂ blackboard_R × blackboard_R start_POSTSUPERSCRIPT italic_n end_POSTSUPERSCRIPT is a trapping isolating segment for ( 28 ) iff for any function g : × n n normal-: 𝑔 normal-→ superscript 𝑛 superscript 𝑛 g:\mathbb{R}\times\mathbb{R}^{n}\to\mathbb{R}^{n} italic_g : blackboard_R × blackboard_R start_POSTSUPERSCRIPT italic_n end_POSTSUPERSCRIPT → blackboard_R start_POSTSUPERSCRIPT italic_n end_POSTSUPERSCRIPT , C 1 superscript 𝐶 1 C^{1} italic_C start_POSTSUPERSCRIPT 1 end_POSTSUPERSCRIPT with respect to x 𝑥 x italic_x , g x 𝑔 𝑥 \frac{\partial g}{\partial x} divide start_ARG ∂ italic_g end_ARG start_ARG ∂ italic_x end_ARG and g 𝑔 g italic_g continuous with respect to t 𝑡 t italic_t , such that g ( t , x ) [ δ ] 𝑔 𝑡 𝑥 delimited-[] 𝛿 g(t,x)\in[\delta] italic_g ( italic_t , italic_x ) ∈ [ italic_δ ] , the set Z 𝑍 Z italic_Z is a trapping isolating segment for the semiprocess induced by

x ( t ) = f ( t , x ( t ) ) + g ( t , x ( t ) ) . superscript 𝑥 𝑡 𝑓 𝑡 𝑥 𝑡 𝑔 𝑡 𝑥 𝑡 x^{\prime}(t)=f(t,x(t))+g(t,x(t)). italic_x start_POSTSUPERSCRIPT ′ end_POSTSUPERSCRIPT ( italic_t ) = italic_f ( italic_t , italic_x ( italic_t ) ) + italic_g ( italic_t , italic_x ( italic_t ) ) . (29)

Definition 2.2 .

On an inner product space ( 𝕍 , ) 𝕍 (\mathbb{V},{\,\cdot\,}) ( blackboard_V , ⋅ ) , a (binary) cross product is a skew-symmetric linear product × : 𝕍 × 𝕍 𝕍 fragments : V V V \boldsymbol{\times}:\mathbb{V}\times\mathbb{V}\to\mathbb{V} bold_× : blackboard_V × blackboard_V → blackboard_V compatible with \cdot , meaning that

  1. (a)

    ( x × y ) x = 0 𝑥 𝑦 𝑥 0 (x\boldsymbol{\times}y)\cdot x=0 ( italic_x bold_× italic_y ) ⋅ italic_x = 0 and

  2. (b)

    ( x × y ) ( x × y ) = ( x x ) ( y y ) - ( x y ) 2 𝑥 𝑦 𝑥 𝑦 𝑥 𝑥 𝑦 𝑦 superscript 𝑥 𝑦 2 (x\boldsymbol{\times}y)\cdot(x\boldsymbol{\times}y)=(x\cdot x)(y\cdot y)-(x% \cdot y)^{2} ( italic_x bold_× italic_y ) ⋅ ( italic_x bold_× italic_y ) = ( italic_x ⋅ italic_x ) ( italic_y ⋅ italic_y ) - ( italic_x ⋅ italic_y ) start_POSTSUPERSCRIPT 2 end_POSTSUPERSCRIPT

for all x , y 𝕍 𝑥 𝑦 𝕍 x,y\in\mathbb{V} italic_x , italic_y ∈ blackboard_V .

Definition 4.7 .

On a manifold M 𝑀 M italic_M with boundary M 𝑀 \partial M ∂ italic_M and interior M i n t subscript 𝑀 𝑖 𝑛 𝑡 M_{int} italic_M start_POSTSUBSCRIPT italic_i italic_n italic_t end_POSTSUBSCRIPT an affine connection \nabla on M i n t subscript 𝑀 𝑖 𝑛 𝑡 M_{int} italic_M start_POSTSUBSCRIPT italic_i italic_n italic_t end_POSTSUBSCRIPT is called projectively compact of order α + 𝛼 subscript \alpha\in\mathbb{R}_{+} italic_α ∈ blackboard_R start_POSTSUBSCRIPT + end_POSTSUBSCRIPT if for any x M 𝑥 𝑀 x\in\partial M italic_x ∈ ∂ italic_M , there is a neighborhood U 𝑈 U italic_U of x 𝑥 x italic_x in M 𝑀 M italic_M and a defining function r : U : 𝑟 𝑈 r:U\to\mathbb{R} italic_r : italic_U → blackboard_R for U M 𝑈 𝑀 U\cap\partial M italic_U ∩ ∂ italic_M such that the connection

(52) ^ = + d r α r ^ 𝑑 𝑟 𝛼 𝑟 \hat{\nabla}=\nabla+\tfrac{dr}{\alpha r} ^ start_ARG ∇ end_ARG = ∇ + divide start_ARG italic_d italic_r end_ARG start_ARG italic_α italic_r end_ARG

on U M i n t 𝑈 subscript 𝑀 𝑖 𝑛 𝑡 U\cap M_{int} italic_U ∩ italic_M start_POSTSUBSCRIPT italic_i italic_n italic_t end_POSTSUBSCRIPT extends to all of U 𝑈 U italic_U . A metric is said to be projectively compact of order α 𝛼 \alpha italic_α if its Levi-Civita connection satisfies this condition.


Definition 1

Let S , T 𝑆 𝑇 S,T italic_S , italic_T be nonempty sets and consider a function f : T × D S normal-: 𝑓 normal-→ 𝑇 𝐷 𝑆 f:T\times D\rightarrow S italic_f : italic_T × italic_D → italic_S where D S × S 𝐷 𝑆 𝑆 D\subset S\times S italic_D ⊂ italic_S × italic_S . Then f 𝑓 f italic_f is semi-invertible or partially invertible if there are sets M D 𝑀 𝐷 M\subset D italic_M ⊂ italic_D , M S × S superscript 𝑀 normal-′ 𝑆 𝑆 M^{\prime}\subset S\times S italic_M start_POSTSUPERSCRIPT ′ end_POSTSUPERSCRIPT ⊂ italic_S × italic_S and a function h : T × M S normal-: normal-→ 𝑇 superscript 𝑀 normal-′ 𝑆 h:T\times M^{\prime}\rightarrow S italic_h : italic_T × italic_M start_POSTSUPERSCRIPT ′ end_POSTSUPERSCRIPT → italic_S such that

w = f ( t , u , v ) v = h ( t , u , w ) for all t T , ( u , v ) M and ( u , w ) M . formulae-sequence 𝑤 𝑓 𝑡 𝑢 𝑣 𝑣 𝑡 𝑢 𝑤 formulae-sequence for all 𝑡 𝑇 𝑢 𝑣 𝑀 and 𝑢 𝑤 superscript 𝑀 w=f(t,u,v)\Rightarrow v=h(t,u,w)\quad\text{for all }t\in T,\text{ }(u,v)\in M% \text{\ and }(u,w)\in M^{\prime}. italic_w = italic_f ( italic_t , italic_u , italic_v ) ⇒ italic_v = italic_h ( italic_t , italic_u , italic_w ) for all italic_t ∈ italic_T , ( italic_u , italic_v ) ∈ italic_M and ( italic_u , italic_w ) ∈ italic_M start_POSTSUPERSCRIPT ′ end_POSTSUPERSCRIPT . (8)

The function h h italic_h may be called a semi-inversion, or partial inversion of f . 𝑓 f. italic_f . If f 𝑓 f italic_f is independent of t 𝑡 t italic_t then t 𝑡 t italic_t is dropped from the above notation (see the examples below).


Definition 1.2 .

In a classical Gauss diagram of degree n 𝑛 n italic_n , the complementary of the arrows is made of 2 n 2 𝑛 2n 2 italic_n oriented components. These are called the edges of the diagram. In a diagram with no arrow, we still call the whole circle an edge.

Let e 𝑒 e italic_e be an edge in a Gauss diagram, between two consecutive arrow ends that do not belong to the same arrow. Put

η ( e ) = { + 1 if the arrows that bound e cross each other - 1 otherwise , 𝜂 𝑒 cases 1 if the arrows that bound e cross each other 1 otherwise \eta(e)=\left\{\begin{array}[]{l}+1\text{ if the arrows that bound $e$ cross % each other}\\ -1\text{ otherwise}\end{array}\right., italic_η ( italic_e ) = { start_ARRAY start_ROW start_CELL + 1 if the arrows that bound italic_e cross each other end_CELL end_ROW start_ROW start_CELL - 1 otherwise end_CELL end_ROW end_ARRAY ,

and let ( e ) absent 𝑒 \uparrow\!\!(e) ↑ ( italic_e ) be the number of arrowheads at the boundary of e 𝑒 e italic_e . Then define

ε ( e ) = η ( e ) ( - 1 ) ( e ) . 𝜀 𝑒 𝜂 𝑒 superscript 1 absent 𝑒 \varepsilon(e)=\eta(e)\cdot(-1)^{\uparrow(e)}. italic_ε ( italic_e ) = italic_η ( italic_e ) ⋅ ( - 1 ) start_POSTSUPERSCRIPT ↑ ( italic_e ) end_POSTSUPERSCRIPT .

Finally, define w ( e ) w 𝑒 \mathrm{w}(e) roman_w ( italic_e ) as the product of the writhes of the two arrows at the boundary of e 𝑒 e italic_e .