Definition 3

A linear operator βˆ‚ : R β†’ R : β†’ 𝑅 𝑅 \partial:R\to R βˆ‚ : italic_R β†’ italic_R is called a divided difference operator if it is not identically trivial and satisfies the following identity

βˆ‚ ⁑ ( x ⁒ y ) = ( βˆ‚ ⁑ x ) ⁒ y + x ⁒ ( βˆ‚ ⁑ y ) - Ξ± ⁒ ( βˆ‚ ⁑ x ) ⁒ ( βˆ‚ ⁑ y ) π‘₯ 𝑦 π‘₯ 𝑦 π‘₯ 𝑦 𝛼 π‘₯ 𝑦 \partial(xy)=(\partial x)y+x(\partial y)-\alpha(\partial x)(\partial y) βˆ‚ ( italic_x italic_y ) = ( βˆ‚ italic_x ) italic_y + italic_x ( βˆ‚ italic_y ) - italic_Ξ± ( βˆ‚ italic_x ) ( βˆ‚ italic_y ) (12)

for all x , y ∈ R π‘₯ 𝑦 𝑅 x,y\in R italic_x , italic_y ∈ italic_R , where Ξ± ∈ R 𝛼 𝑅 \alpha\in R italic_Ξ± ∈ italic_R is not invertible in R 𝑅 R italic_R .

Definition 4

An algebra over R 𝑅 R italic_R additively isomorphic to R ⁒ [ t ] 𝑅 delimited-[] 𝑑 R[t] italic_R [ italic_t ] is called an Ore extension if R βŠ‚ R ⁒ [ t ] 𝑅 𝑅 delimited-[] 𝑑 R\subset R[t] italic_R βŠ‚ italic_R [ italic_t ] and

t ⁒ a = Ο• ⁒ ( a ) ⁒ t + Ξ΄ ⁒ ( a ) . 𝑑 π‘Ž italic-Ο• π‘Ž 𝑑 𝛿 π‘Ž ta=\phi(a)t+\delta(a). italic_t italic_a = italic_Ο• ( italic_a ) italic_t + italic_Ξ΄ ( italic_a ) . (19)

The operator Ο• italic-Ο• \phi italic_Ο• from ( 19 ) is called Ore’s Ο• italic-Ο• \phi italic_Ο• -derivation.


Definition 1

A trialgebra ( A , * , Ξ” , β‹… ) 𝐴 normal-Ξ” normal-β‹… (A,*,\Delta,\cdot) ( italic_A , * , roman_Ξ” , β‹… ) with * * * and β‹… normal-β‹… \cdot β‹… associative products on A 𝐴 A italic_A (where * * * may be partially defined, only) and Ξ” normal-Ξ” \Delta roman_Ξ” a coassociative coproduct on A 𝐴 A italic_A is given if both ( A , * , Ξ” ) 𝐴 normal-Ξ” (A,*,\Delta) ( italic_A , * , roman_Ξ” ) and ( A , β‹… , Ξ” ) 𝐴 normal-β‹… normal-Ξ” (A,\cdot,\Delta) ( italic_A , β‹… , roman_Ξ” ) are bialgebras and the following compatibility condition between the products is satisfied for arbitrary elements a , b , c , d ∈ A π‘Ž 𝑏 𝑐 𝑑 𝐴 a,b,c,d\in A italic_a , italic_b , italic_c , italic_d ∈ italic_A :

( a * b ) β‹… ( c * d ) = ( a β‹… c ) * ( b β‹… d ) β‹… π‘Ž 𝑏 𝑐 𝑑 β‹… π‘Ž 𝑐 β‹… 𝑏 𝑑 (a*b)\cdot(c*d)=(a\cdot c)*(b\cdot d) ( italic_a * italic_b ) β‹… ( italic_c * italic_d ) = ( italic_a β‹… italic_c ) * ( italic_b β‹… italic_d )

whenever both sides are defined.


Definition 5.4 .

For two mapping classes f , h ∈ β„³ g , b , n 𝑓 β„Ž subscript β„³ 𝑔 𝑏 𝑛 f,h\in{\cal M}_{g,b,n} italic_f , italic_h ∈ caligraphic_M start_POSTSUBSCRIPT italic_g , italic_b , italic_n end_POSTSUBSCRIPT , we let

i ⁒ ( f , h ) = i ⁒ ( Οƒ ⁒ ( f ) , Οƒ ⁒ ( h ) ) . 𝑖 𝑓 β„Ž 𝑖 𝜎 𝑓 𝜎 β„Ž i(f,h)=i({\sigma}(f),{\sigma}(h)). italic_i ( italic_f , italic_h ) = italic_i ( italic_Οƒ ( italic_f ) , italic_Οƒ ( italic_h ) ) .

Definition 4.5 .

Let b ∈ H 𝑏 𝐻 b\in H italic_b ∈ italic_H , where H 𝐻 H italic_H is canonically identified with H * * superscript 𝐻 absent H^{**} italic_H start_POSTSUPERSCRIPT * * end_POSTSUPERSCRIPT , be the left modular function defined by

(29) b = Ξ· ∘ Ξ½ * 𝑏 πœ‚ superscript 𝜈 b=\eta\circ\nu^{*} italic_b = italic_Ξ· ∘ italic_Ξ½ start_POSTSUPERSCRIPT * end_POSTSUPERSCRIPT

where Ξ· πœ‚ \eta italic_Ξ· is the counit of H * superscript 𝐻 H^{*} italic_H start_POSTSUPERSCRIPT * end_POSTSUPERSCRIPT defined by Ξ· ⁒ ( f ) = f ⁒ ( 1 ) πœ‚ 𝑓 𝑓 1 \eta(f)=f(1) italic_Ξ· ( italic_f ) = italic_f ( 1 ) for every f ∈ H * 𝑓 superscript 𝐻 f\in H^{*} italic_f ∈ italic_H start_POSTSUPERSCRIPT * end_POSTSUPERSCRIPT .