Definition 2.4 .

If f ( x ) 𝑓 𝑥 f(x) italic_f ( italic_x ) is a real-valued analytic function of x 𝑥 x italic_x in a neighborhood of a 𝑎 a italic_a , we define the sign of f 𝑓 f italic_f at a 𝑎 a italic_a sgn ( f , a ) sgn 𝑓 𝑎 \operatorname{sgn}(f,a) roman_sgn ( italic_f , italic_a ) to be the sign of the first nonvanishing Taylor series coefficient (around a 𝑎 a italic_a ), if there is such, and zero otherwise. In other words, if f 0 𝑓 0 f\neq 0 italic_f ≠ 0 , we have:

sgn ( f , a ) = sgn ( f ( n ) ( a ) ) { - 1 , 1 } , sgn 𝑓 𝑎 sgn superscript 𝑓 𝑛 𝑎 1 1 \operatorname{sgn}(f,a)=\operatorname{sgn}(f^{(n)}(a))\,\in\{-1,1\}, roman_sgn ( italic_f , italic_a ) = roman_sgn ( italic_f start_POSTSUPERSCRIPT ( italic_n ) end_POSTSUPERSCRIPT ( italic_a ) ) ∈ { - 1 , 1 } ,

where f ( k ) ( a ) = 0 superscript 𝑓 𝑘 𝑎 0 f^{(k)}(a)=0 italic_f start_POSTSUPERSCRIPT ( italic_k ) end_POSTSUPERSCRIPT ( italic_a ) = 0 for k < n 𝑘 𝑛 k<n italic_k < italic_n and f ( n ) ( a ) 0 superscript 𝑓 𝑛 𝑎 0 f^{(n)}(a)\neq 0 italic_f start_POSTSUPERSCRIPT ( italic_n ) end_POSTSUPERSCRIPT ( italic_a ) ≠ 0 .


Definition 2.1

A Courant algebroid is a vector bundle E M normal-→ 𝐸 𝑀 E\to M italic_E → italic_M with a Loday bracket on Γ E normal-Γ 𝐸 \Gamma E roman_Γ italic_E , i.e., an \mathbb{R} blackboard_R -bilinear map satisfying the Jacobi identity,

[ x , [ y , z ] ] = [ [ x , y ] , z ] + [ y , [ x , z ] ] , 𝑥 𝑦 𝑧 𝑥 𝑦 𝑧 𝑦 𝑥 𝑧 [x,[y,z]]=[[x,y],z]+[y,[x,z]]\ , [ italic_x , [ italic_y , italic_z ] ] = [ [ italic_x , italic_y ] , italic_z ] + [ italic_y , [ italic_x , italic_z ] ] ,

for all x , y , z Γ E 𝑥 𝑦 𝑧 normal-Γ 𝐸 x,y,z\in\Gamma E italic_x , italic_y , italic_z ∈ roman_Γ italic_E , an anchor, ρ : E T M normal-: 𝜌 normal-→ 𝐸 𝑇 𝑀 \rho:E\to TM italic_ρ : italic_E → italic_T italic_M , which is a morphism of vector bundles, and a field of non-degenerate symmetric bilinear forms ( | ) fragments normal-( normal-| normal-) (~{}|~{}) ( | ) on the fibers of E 𝐸 E italic_E , satisfying

( i ) ρ ( x ) ( u | v ) i 𝜌 𝑥 conditional 𝑢 𝑣 \displaystyle{\rm(i)}\quad\quad\quad\rho(x)(u|v) ( roman_i ) italic_ρ ( italic_x ) ( italic_u | italic_v ) = ( x | [ u , v ] + [ v , u ] ) , absent conditional 𝑥 𝑢 𝑣 𝑣 𝑢 \displaystyle=(x~{}|~{}[u,v]+[v,u])\ , = ( italic_x | [ italic_u , italic_v ] + [ italic_v , italic_u ] ) ,
( ii ) ρ ( x ) ( u | v ) ii 𝜌 𝑥 conditional 𝑢 𝑣 \displaystyle{\rm(ii)}\quad\quad\quad\rho(x)(u|v) ( roman_ii ) italic_ρ ( italic_x ) ( italic_u | italic_v ) = ( [ x , u ] | v ) + ( u | [ x , v ] ) , absent conditional 𝑥 𝑢 𝑣 conditional 𝑢 𝑥 𝑣 \displaystyle=([x,u]~{}|~{}v)+(u~{}|~{}[x,v])\ , = ( [ italic_x , italic_u ] | italic_v ) + ( italic_u | [ italic_x , italic_v ] ) ,

for all x 𝑥 x italic_x , u 𝑢 u italic_u and v Γ E 𝑣 normal-Γ 𝐸 v\in\Gamma E italic_v ∈ roman_Γ italic_E .


Definition 1.5

A Poisson algebra A 𝐴 A italic_A over k 𝑘 k italic_k is called exact if there exists a derivation ξ : A A normal-: 𝜉 normal-→ 𝐴 𝐴 \xi:A\to A italic_ξ : italic_A → italic_A such that

(1.3) ξ ( { a , b } ) = { a , b } + { ξ ( a ) , b } + { a , ξ ( b ) } 𝜉 𝑎 𝑏 𝑎 𝑏 𝜉 𝑎 𝑏 𝑎 𝜉 𝑏 \xi(\{a,b\})=\{a,b\}+\{\xi(a),b\}+\{a,\xi(b)\} italic_ξ ( { italic_a , italic_b } ) = { italic_a , italic_b } + { italic_ξ ( italic_a ) , italic_b } + { italic_a , italic_ξ ( italic_b ) }

for any a , b A 𝑎 𝑏 𝐴 a,b\in A italic_a , italic_b ∈ italic_A .


Definition 2

A Lie algebroid ( E , ρ , [ , ] ) 𝐸 𝜌 normal-⋅ normal-⋅ (E,\rho,[\cdot,\cdot]) ( italic_E , italic_ρ , [ ⋅ , ⋅ ] ) is a vector bundle π : E M normal-: 𝜋 normal-→ 𝐸 𝑀 \pi\colon E\to M italic_π : italic_E → italic_M together with a bundle map (“anchor”) ρ : E T M normal-: 𝜌 normal-→ 𝐸 𝑇 𝑀 \rho\colon E\to TM italic_ρ : italic_E → italic_T italic_M and a Lie algebra structure [ , ] : Γ ( E ) × Γ ( E ) Γ ( E ) normal-: normal-⋅ normal-⋅ normal-→ normal-Γ 𝐸 normal-Γ 𝐸 normal-Γ 𝐸 [\cdot,\cdot]\colon\Gamma(E)\times\Gamma(E)\to\Gamma(E) [ ⋅ , ⋅ ] : roman_Γ ( italic_E ) × roman_Γ ( italic_E ) → roman_Γ ( italic_E ) satisfying the Leibniz identity

[ ψ , f ψ ] = f [ ψ , ψ ] + ( ρ ( ψ ) f ) ψ 𝜓 𝑓 superscript 𝜓 𝑓 𝜓 superscript 𝜓 𝜌 𝜓 𝑓 superscript 𝜓 [\psi,f\psi^{\prime}]=f[\psi,\psi^{\prime}]+\left(\rho(\psi)f\right)\psi^{\prime} [ italic_ψ , italic_f italic_ψ start_POSTSUPERSCRIPT ′ end_POSTSUPERSCRIPT ] = italic_f [ italic_ψ , italic_ψ start_POSTSUPERSCRIPT ′ end_POSTSUPERSCRIPT ] + ( italic_ρ ( italic_ψ ) italic_f ) italic_ψ start_POSTSUPERSCRIPT ′ end_POSTSUPERSCRIPT (9)

ψ , ψ Γ ( E ) , f C ( M ) formulae-sequence for-all 𝜓 superscript 𝜓 Γ 𝐸 for-all 𝑓 superscript 𝐶 𝑀 \forall\psi,\psi^{\prime}\in\Gamma(E),\forall f\in C^{\infty}(M) ∀ italic_ψ , italic_ψ start_POSTSUPERSCRIPT ′ end_POSTSUPERSCRIPT ∈ roman_Γ ( italic_E ) , ∀ italic_f ∈ italic_C start_POSTSUPERSCRIPT ∞ end_POSTSUPERSCRIPT ( italic_M ) .


Definition 2.1

A Poisson manifold ( M , { , } ) 𝑀 normal-⋅ normal-⋅ (M,\{\cdot,\cdot\}) ( italic_M , { ⋅ , ⋅ } ) is a manifold endowed with a Poisson bracket, that is a bilinear antisymmetric composition laws defined on the space C ( M ) superscript 𝐶 𝑀 C^{\infty}(M) italic_C start_POSTSUPERSCRIPT ∞ end_POSTSUPERSCRIPT ( italic_M ) satisfying:

  1. 1.

    The Leibnitz rule: { f g , h } = f { g , h } + g { f , h } 𝑓 𝑔 𝑓 𝑔 𝑔 𝑓 \{fg,h\}=f\{g,h\}+g\{f,h\} { italic_f italic_g , italic_h } = italic_f { italic_g , italic_h } + italic_g { italic_f , italic_h } ;

  2. 2.

    The Jacobi identity { f , { g , h } } + { g , { h , f } } + { h , { f , g } } = 0 𝑓 𝑔 𝑔 𝑓 𝑓 𝑔 0 \{f,\{g,h\}\}+\{g,\{h,f\}\}+\{h,\{f,g\}\}=0 { italic_f , { italic_g , italic_h } } + { italic_g , { italic_h , italic_f } } + { italic_h , { italic_f , italic_g } } = 0 .


Definition 2.1 .

An orthomodular lattice ( OML ) is an algebraic structure L , , fragments normal-⟨ L normal-, superscript normal-, perpendicular-to normal-⟩ \langle L,\cup,^{\perp}\rangle ⟨ italic_L , ∪ , start_POSTSUPERSCRIPT ⟂ end_POSTSUPERSCRIPT ⟩ in which the following conditions are satisfied for any a , b , c L 𝑎 𝑏 𝑐 𝐿 a,b,c\in L italic_a , italic_b , italic_c ∈ italic_L :

L1. a a & a a formulae-sequence 𝑎 superscript 𝑎 perpendicular-to absent perpendicular-to superscript 𝑎 perpendicular-to absent perpendicular-to 𝑎 a\leq a^{\perp\perp}\quad\&\quad a^{\perp\perp}\leq a italic_a ≤ italic_a start_POSTSUPERSCRIPT ⟂ ⟂ end_POSTSUPERSCRIPT & italic_a start_POSTSUPERSCRIPT ⟂ ⟂ end_POSTSUPERSCRIPT ≤ italic_a

L2. a a b & b a b formulae-sequence 𝑎 𝑎 𝑏 𝑏 𝑎 𝑏 a\leq a\cup b\quad\&\quad b\leq a\cup b italic_a ≤ italic_a ∪ italic_b & italic_b ≤ italic_a ∪ italic_b

L3. a b & b a a = b formulae-sequence 𝑎 𝑏 formulae-sequence 𝑏 𝑎 normal-⇒ 𝑎 𝑏 a\leq b\quad\&\quad b\leq a\quad\Rightarrow\quad a=b italic_a ≤ italic_b & italic_b ≤ italic_a ⇒ italic_a = italic_b

L4. a 1 𝑎 1 a\leq 1 italic_a ≤ 1

L5. a b b a formulae-sequence 𝑎 𝑏 normal-⇒ superscript 𝑏 perpendicular-to superscript 𝑎 perpendicular-to a\leq b\quad\Rightarrow\quad b^{\perp}\leq a^{\perp} italic_a ≤ italic_b ⇒ italic_b start_POSTSUPERSCRIPT ⟂ end_POSTSUPERSCRIPT ≤ italic_a start_POSTSUPERSCRIPT ⟂ end_POSTSUPERSCRIPT

L6. a b & b c a c formulae-sequence 𝑎 𝑏 formulae-sequence 𝑏 𝑐 normal-⇒ 𝑎 𝑐 a\leq b\quad\&\quad b\leq c\quad\Rightarrow\quad a\leq c italic_a ≤ italic_b & italic_b ≤ italic_c ⇒ italic_a ≤ italic_c

L7. a c & b c a b c formulae-sequence 𝑎 𝑐 formulae-sequence 𝑏 𝑐 normal-⇒ 𝑎 𝑏 𝑐 a\leq c\quad\&\quad b\leq c\quad\Rightarrow\quad a\cup b\leq c italic_a ≤ italic_c & italic_b ≤ italic_c ⇒ italic_a ∪ italic_b ≤ italic_c

L8. a i b = 1 subscript normal-→ 𝑖 𝑎 𝑏 1 a\rightarrow_{i}b\>=\>1 italic_a → start_POSTSUBSCRIPT italic_i end_POSTSUBSCRIPT italic_b = 1 normal-⇒ \qquad\Rightarrow\qquad a b ( i = 1 , , 5 ) fragments a b italic- fragments normal-( i 1 normal-, normal-… normal-, 5 normal-) a\leq b\qquad\qquad(i=1,\!...,5) italic_a ≤ italic_b ( italic_i = 1 , … , 5 )

where a b def a b = b 𝑎 𝑏 superscript normal-⇔ normal-def 𝑎 𝑏 𝑏 a\leq b{\buildrel\rm def\over{\Leftrightarrow}}a\cup b=b italic_a ≤ italic_b start_RELOP SUPERSCRIPTOP start_ARG ⇔ end_ARG start_ARG roman_def end_ARG end_RELOP italic_a ∪ italic_b = italic_b , 1 = def a a superscript normal-def 1 𝑎 superscript 𝑎 perpendicular-to 1\ {\buildrel\rm def\over{=}}\ a\cup a^{\perp} 1 start_RELOP SUPERSCRIPTOP start_ARG = end_ARG start_ARG roman_def end_ARG end_RELOP italic_a ∪ italic_a start_POSTSUPERSCRIPT ⟂ end_POSTSUPERSCRIPT . Also

a b = def ( a b ) , 0 = def a a . formulae-sequence superscript def 𝑎 𝑏 superscript superscript 𝑎 perpendicular-to superscript 𝑏 perpendicular-to perpendicular-to superscript def 0 𝑎 superscript 𝑎 perpendicular-to a\cap b\ {\buildrel\rm def\over{=}}\ (a^{\perp}\cup b^{\perp})^{\perp},\qquad 0% \ {\buildrel\rm def\over{=}}\ a\cap a^{\perp}. italic_a ∩ italic_b start_RELOP SUPERSCRIPTOP start_ARG = end_ARG start_ARG roman_def end_ARG end_RELOP ( italic_a start_POSTSUPERSCRIPT ⟂ end_POSTSUPERSCRIPT ∪ italic_b start_POSTSUPERSCRIPT ⟂ end_POSTSUPERSCRIPT ) start_POSTSUPERSCRIPT ⟂ end_POSTSUPERSCRIPT , 0 start_RELOP SUPERSCRIPTOP start_ARG = end_ARG start_ARG roman_def end_ARG end_RELOP italic_a ∩ italic_a start_POSTSUPERSCRIPT ⟂ end_POSTSUPERSCRIPT .

and the implications a i b ( i = 1 , , 5 ) fragments a subscript normal-→ 𝑖 b fragments normal-( i 1 normal-, normal-… normal-, 5 normal-) a\rightarrow_{i}b\ (i=1,\dots,5) italic_a → start_POSTSUBSCRIPT italic_i end_POSTSUBSCRIPT italic_b ( italic_i = 1 , … , 5 ) are defined as follows

a 1 b = def a ( a b ) subscript 1 𝑎 𝑏 superscript def superscript 𝑎 perpendicular-to 𝑎 𝑏 a\rightarrow_{1}b\ \ {\buildrel\rm def\over{=}}\ \ a^{\perp}\cup(a\cap b) italic_a → start_POSTSUBSCRIPT 1 end_POSTSUBSCRIPT italic_b start_RELOP SUPERSCRIPTOP start_ARG = end_ARG start_ARG roman_def end_ARG end_RELOP italic_a start_POSTSUPERSCRIPT ⟂ end_POSTSUPERSCRIPT ∪ ( italic_a ∩ italic_b ) (Sasaki)

a 2 b = def b ( a b ) subscript 2 𝑎 𝑏 superscript def 𝑏 superscript 𝑎 perpendicular-to superscript 𝑏 perpendicular-to a\rightarrow_{2}b\ \ {\buildrel\rm def\over{=}}\ \ b\cup(a^{\perp}\cap b^{% \perp}) italic_a → start_POSTSUBSCRIPT 2 end_POSTSUBSCRIPT italic_b start_RELOP SUPERSCRIPTOP start_ARG = end_ARG start_ARG roman_def end_ARG end_RELOP italic_b ∪ ( italic_a start_POSTSUPERSCRIPT ⟂ end_POSTSUPERSCRIPT ∩ italic_b start_POSTSUPERSCRIPT ⟂ end_POSTSUPERSCRIPT ) (Dishkant)

a 3 b = def ( ( a b ) ( a b ) ) ( a ( a b ) ) subscript 3 𝑎 𝑏 superscript def superscript 𝑎 perpendicular-to 𝑏 superscript 𝑎 perpendicular-to superscript 𝑏 perpendicular-to 𝑎 superscript 𝑎 perpendicular-to 𝑏 a\rightarrow_{3}b\ \ {\buildrel\rm def\over{=}}\ \ ((a^{\perp}\cap b)\cup(a^{% \perp}\cap b^{\perp}))\cup\bigl{(}a\cap(a^{\perp}\cup b)\bigr{)} italic_a → start_POSTSUBSCRIPT 3 end_POSTSUBSCRIPT italic_b start_RELOP SUPERSCRIPTOP start_ARG = end_ARG start_ARG roman_def end_ARG end_RELOP ( ( italic_a start_POSTSUPERSCRIPT ⟂ end_POSTSUPERSCRIPT ∩ italic_b ) ∪ ( italic_a start_POSTSUPERSCRIPT ⟂ end_POSTSUPERSCRIPT ∩ italic_b start_POSTSUPERSCRIPT ⟂ end_POSTSUPERSCRIPT ) ) ∪ ( italic_a ∩ ( italic_a start_POSTSUPERSCRIPT ⟂ end_POSTSUPERSCRIPT ∪ italic_b ) ) (Kalmbach)

a 4 b = def ( ( a b ) ( a b ) ) ( ( a b ) b ) subscript 4 𝑎 𝑏 superscript def 𝑎 𝑏 superscript 𝑎 perpendicular-to 𝑏 superscript 𝑎 perpendicular-to 𝑏 superscript 𝑏 perpendicular-to a\rightarrow_{4}b\ \ {\buildrel\rm def\over{=}}\ \ ((a\cap b)\cup(a^{\perp}% \cap b))\cup\bigl{(}(a^{\perp}\cup b)\cap b^{\perp}\bigr{)} italic_a → start_POSTSUBSCRIPT 4 end_POSTSUBSCRIPT italic_b start_RELOP SUPERSCRIPTOP start_ARG = end_ARG start_ARG roman_def end_ARG end_RELOP ( ( italic_a ∩ italic_b ) ∪ ( italic_a start_POSTSUPERSCRIPT ⟂ end_POSTSUPERSCRIPT ∩ italic_b ) ) ∪ ( ( italic_a start_POSTSUPERSCRIPT ⟂ end_POSTSUPERSCRIPT ∪ italic_b ) ∩ italic_b start_POSTSUPERSCRIPT ⟂ end_POSTSUPERSCRIPT ) (non-tollens)

a 5 b = def ( ( a b ) ( a b ) ) ( a b ) subscript 5 𝑎 𝑏 superscript def 𝑎 𝑏 superscript 𝑎 perpendicular-to 𝑏 superscript 𝑎 perpendicular-to superscript 𝑏 perpendicular-to a\rightarrow_{5}b\ \ {\buildrel\rm def\over{=}}\ \ ((a\cap b)\cup(a^{\perp}% \cap b))\cup(a^{\perp}\cap b^{\perp}) italic_a → start_POSTSUBSCRIPT 5 end_POSTSUBSCRIPT italic_b start_RELOP SUPERSCRIPTOP start_ARG = end_ARG start_ARG roman_def end_ARG end_RELOP ( ( italic_a ∩ italic_b ) ∪ ( italic_a start_POSTSUPERSCRIPT ⟂ end_POSTSUPERSCRIPT ∩ italic_b ) ) ∪ ( italic_a start_POSTSUPERSCRIPT ⟂ end_POSTSUPERSCRIPT ∩ italic_b start_POSTSUPERSCRIPT ⟂ end_POSTSUPERSCRIPT ) (relevance)


Definition 1.2 .

A character φ 𝜑 \varphi italic_φ of a graded Hopf algebra {\mathcal{H}} caligraphic_H is said to be even if

φ ¯ = φ ¯ 𝜑 𝜑 \bar{\varphi}=\varphi ¯ start_ARG italic_φ end_ARG = italic_φ

and it is said to be odd if

φ ¯ = φ - 1 . ¯ 𝜑 superscript 𝜑 1 \bar{\varphi}=\varphi^{-1}\,. ¯ start_ARG italic_φ end_ARG = italic_φ start_POSTSUPERSCRIPT - 1 end_POSTSUPERSCRIPT .

Definition 2 (Quaternion Algebras) .

Let F 𝐹 F italic_F be a field of characteristic 2 absent 2 \neq~{}2 ≠ 2 . For a , b F * 𝑎 𝑏 superscript 𝐹 a,b\in F^{*} italic_a , italic_b ∈ italic_F start_POSTSUPERSCRIPT * end_POSTSUPERSCRIPT , let H ( a , b ) 𝐻 𝑎 𝑏 H(a,b) italic_H ( italic_a , italic_b ) be the F 𝐹 F italic_F -algebra with basis 1 , i , j , k 1 𝑖 𝑗 𝑘 1,i,j,k 1 , italic_i , italic_j , italic_k (as an F 𝐹 F italic_F -vector space) and with multiplication rules

i 2 = a , j 2 = b , i j = k = - j i . formulae-sequence superscript 𝑖 2 𝑎 formulae-sequence superscript 𝑗 2 𝑏 𝑖 𝑗 𝑘 𝑗 𝑖 i^{2}=a,j^{2}=b,ij=k=-ji. italic_i start_POSTSUPERSCRIPT 2 end_POSTSUPERSCRIPT = italic_a , italic_j start_POSTSUPERSCRIPT 2 end_POSTSUPERSCRIPT = italic_b , italic_i italic_j = italic_k = - italic_j italic_i .

Then H ( a , b ) 𝐻 𝑎 𝑏 H(a,b) italic_H ( italic_a , italic_b ) is an F 𝐹 F italic_F -algebra which is called a quaternion algebra over F 𝐹 F italic_F .


Definition 1.1

A Poisson algebra over the field k 𝑘 k italic_k is a commutative algebra A 𝐴 A italic_A over k 𝑘 k italic_k equipped with an additional skew-linear operation { - , - } : A A A normal-: normal-→ tensor-product 𝐴 𝐴 𝐴 \{-,-\}:A\otimes A\to A { - , - } : italic_A ⊗ italic_A → italic_A such that

(1.1) { a , b c } = { a , b } c + { a , c } b , 0 = { a , { b , c } } + { b , { c , a } } + { c , { a , b } } , fragments fragments { a , b c } fragments { a , b } c fragments { a , c } b italic- , 0 fragments { a , fragments { b , c } } fragments { b , fragments { c , a } } fragments { c , fragments { a , b } } , \{a,bc\}=\{a,b\}c+\{a,c\}b\quad,\quad 0=\{a,\{b,c\}\}+\{b,\{c,a\}\}+\{c,\{a,b% \}\}, { italic_a , italic_b italic_c } = { italic_a , italic_b } italic_c + { italic_a , italic_c } italic_b , 0 = { italic_a , { italic_b , italic_c } } + { italic_b , { italic_c , italic_a } } + { italic_c , { italic_a , italic_b } } ,

for all a , b , c A 𝑎 𝑏 𝑐 𝐴 a,b,c\in A italic_a , italic_b , italic_c ∈ italic_A . An ideal I A 𝐼 𝐴 I\subset A italic_I ⊂ italic_A is called a Poisson ideal if { i , a } I 𝑖 𝑎 𝐼 \{i,a\}\in I { italic_i , italic_a } ∈ italic_I for any i I 𝑖 𝐼 i\in I italic_i ∈ italic_I , a A 𝑎 𝐴 a\in A italic_a ∈ italic_A .