8.2.7. Functoriality
Consider f : Z → Z ′ f:Z\to Z^{\prime} a morphism of curves and
assume f ∘ ξ 1 + f\circ\xi_{1}^{+} is outgoing for Z ′ Z^{\prime} and f ∘ ξ 2 − f\circ\xi_{2}^{-} is incoming for Z ′ Z^{\prime} .
The morphism f f extends uniquely to a morphism of curves f : Z ξ → Z f ∘ ξ ′ f:Z_{\xi}\to Z^{\prime}_{f\circ\xi} .
The functor f : 𝒮 f , M ∙ ( Z ) → 𝒮 f ( M ) ∙ ( Z ′ ) f:{\mathcal{S}}^{\bullet}_{f,M}(Z)\to{\mathcal{S}}^{\bullet}_{f(M)}(Z^{\prime}) can be equipped with a structure of morphism
of 2 2 -representations L ξ 1 + ∙ → L f ∘ ξ 1 + ∙ L_{\xi_{1}^{+}}^{\bullet}\to L_{f\circ\xi_{1}^{+}}^{\bullet} and
of morphism of 2 2 -representations R ξ 2 − ∙ → R f ∘ ξ 2 − ∙ R_{\xi_{2}^{-}}^{\bullet}\to R_{f\circ\xi_{2}^{-}}^{\bullet}
(Lemma 8.1.7 and §8.1.5 ),
and it induces a differential pointed functor
(cf §4.3.4 )
Δ f : Δ R ξ 2 − , L ξ 1 + , λ 𝒮 f , M ∙ ( Z ) → Δ R f ∘ ξ 2 − , L f ∘ ξ 1 + , λ ′ 𝒮 f ( M ) ∙ ( Z ′ ) , \Delta f:\Delta_{R_{\xi_{2}^{-}},L_{\xi_{1}^{+}},\lambda}{\mathcal{S}}^{\bullet}_{f,M}(Z)\to\Delta_{R_{f\circ\xi_{2}^{-}},L_{f\circ\xi_{1}^{+}},\lambda^{\prime}}{\mathcal{S}}^{\bullet}_{f(M)}(Z^{\prime}),
where λ ′ \lambda^{\prime} is the analog of the map λ \lambda for Z ′ Z^{\prime} .
We obtain a commutative diagram of differential pointed functors
(8.2.1)
Δ R ξ 2 − , L ξ 1 + , λ 𝒮 f , M ∙ ( Z ) \textstyle{\Delta_{R_{\xi_{2}^{-}},L_{\xi_{1}^{+}},\lambda}{\mathcal{S}}^{\bullet}_{f,M}(Z)\ignorespaces\ignorespaces\ignorespaces\ignorespaces\ignorespaces\ignorespaces\ignorespaces\ignorespaces} Ξ \scriptstyle{\Xi} Δ f \scriptstyle{\Delta f} 𝒮 f , M ∙ ( Z ξ ) \textstyle{{\mathcal{S}}^{\bullet}_{f,M}(Z_{\xi})\ignorespaces\ignorespaces\ignorespaces\ignorespaces} f \scriptstyle{f} Δ R f ∘ ξ 2 − , L f ∘ ξ 1 + , λ ′ 𝒮 f ( M ) ∙ ( Z ′ ) \textstyle{\Delta_{R_{f\circ\xi_{2}^{-}},L_{f\circ\xi_{1}^{+}},\lambda^{\prime}}{\mathcal{S}}^{\bullet}_{f(M)}(Z^{\prime})\ignorespaces\ignorespaces\ignorespaces\ignorespaces} Ξ \scriptstyle{\Xi} 𝒮 f ( M ) ∙ ( Z f ∘ ξ ′ ) \textstyle{{\mathcal{S}}^{\bullet}_{f(M)}(Z^{\prime}_{f\circ\xi})}
Assume f | Z f_{|Z} is strict. It follows that f f is strict.
The functor f # : add ( 𝒮 f ( M ) ( Z ′ ) ) → add ( 𝒮 M ( Z ) ) f^{\#}:\operatorname{add}\nolimits({\mathcal{S}}_{f(M)}(Z^{\prime}))\to\operatorname{add}\nolimits({\mathcal{S}}_{M}(Z)) can be equipped with a structure of morphism
of 2 2 -representations L f ∘ ξ 1 + → L ξ 1 + L_{f\circ\xi_{1}^{+}}\to L_{\xi_{1}^{+}} and
of morphism of 2 2 -representations R f ∘ ξ 2 − → R ξ 2 − R_{f\circ\xi_{2}^{-}}\to R_{\xi_{2}^{-}}
(Lemma 8.1.4 and §8.1.5 ),
and it induces a differential functor
(cf §4.3.4 )
Δ f # : Δ R f ∘ ξ 2 − , L f ∘ ξ 1 + , λ ′ add ( 𝒮 f ( M ) ( Z ′ ) ) → Δ R ξ 2 − , L ξ 1 + , λ add ( 𝒮 M ( Z ) ) . \Delta f^{\#}:\Delta_{R_{f\circ\xi_{2}^{-}},L_{f\circ\xi_{1}^{+}},\lambda^{\prime}}\operatorname{add}\nolimits({\mathcal{S}}_{f(M)}(Z^{\prime}))\to\Delta_{R_{\xi_{2}^{-}},L_{\xi_{1}^{+}},\lambda}\operatorname{add}\nolimits({\mathcal{S}}_{M}(Z)).
We obtain a commutative diagram of differential functors
commuting with coproducts
(8.2.2)
Δ R ξ 2 − , L ξ 1 + , λ add ( 𝒮 M ( Z ) ) \textstyle{\Delta_{R_{\xi_{2}^{-}},L_{\xi_{1}^{+}},\lambda}\operatorname{add}\nolimits({\mathcal{S}}_{M}(Z))\ignorespaces\ignorespaces\ignorespaces\ignorespaces} Ξ \scriptstyle{\Xi} add ( 𝒮 M ( Z ξ ) ) \textstyle{\operatorname{add}\nolimits({\mathcal{S}}_{M}(Z_{\xi}))} Δ R f ∘ ξ 2 − , L f ∘ ξ 1 + , λ ′ add ( 𝒮 f ( M ) ( Z ′ ) ) \textstyle{\Delta_{R_{f\circ\xi_{2}^{-}},L_{f\circ\xi_{1}^{+}},\lambda^{\prime}}\operatorname{add}\nolimits({\mathcal{S}}_{f(M)}(Z^{\prime}))\ignorespaces\ignorespaces\ignorespaces\ignorespaces\ignorespaces\ignorespaces\ignorespaces\ignorespaces} Ξ \scriptstyle{\Xi} Δ f # \scriptstyle{\Delta f^{\#}} OPEN add ( 𝒮 f ( M ) ( Z f ∘ ξ ′ ) ) ) \textstyle{\operatorname{add}\nolimits({\mathcal{S}}_{f(M)}(Z^{\prime}_{f\circ\xi})))\ignorespaces\ignorespaces\ignorespaces\ignorespaces} f # \scriptstyle{f^{\#}}