Documentation

LeanPool.RegtsSevenster.RS.Classical.Deligne.FibreMonoidal

The fibre functor is symmetric monoidal #

Deligne's ω is base change to the algebra followed by realization, and its monoidal comparison RS.fibreMu is, on the generators of the tensor product of super modules, nothing but the free-module shuffle evaluated at a pair of morphisms. The three coherence laws of a lax monoidal functor therefore reduce, family by family, to the three coherence laws of the shuffle recorded in RS.FreeModShuffleCoh.

The reduction is uniform. Each generator family names a morphism s out of the intended source into a tensor product of the two sources involved, and the comparison sends a pair (m, n) to s ≫ (m ⊗ₘ n) ≫ freeModShuffle. Associativity at a family is then the associativity of the shuffle conjugated by the coherence identity relating the four s's of that family — exactly the identity that already appears in the corresponding associativity axiom of RS.gammaModule. Unitality and the braiding law are the same computation one factor shorter.

Two signs appear, and both are forced by the target rather than by the fibre functor:

In both places the sign is supplied by RS.OddLine.braid_neg: the self-braiding of the odd line is −1, so the source identification L.sq.inv picks up exactly that sign when the two odd generators are exchanged. No sign is left over.

The functor is packaged as CategoryTheory.Functor.LaxMonoidal and CategoryTheory.Functor.LaxBraided. Invertibility of fibreMu is a separate matter and is not assumed here, so the strong notions Functor.Monoidal and Functor.Braided are not instantiated.

Splitting a tensor of composites #

The coherence of the shuffle at arbitrary sources #

theorem RS.freeModShuffle_assoc_at {D : Type u} [CategoryTheory.Category.{v, u} D] [CategoryTheory.MonoidalCategory D] [CategoryTheory.BraidedCategory D] (R : D) [CategoryTheory.MonObj R] {A B C T T' T'' : D} (s₁ : T ⟶ CategoryTheory.MonoidalCategoryStruct.tensorObj T' C) (s₂ : T' ⟶ CategoryTheory.MonoidalCategoryStruct.tensorObj A B) (s₃ : T ⟶ CategoryTheory.MonoidalCategoryStruct.tensorObj A T'') (s₄ : T'' ⟶ CategoryTheory.MonoidalCategoryStruct.tensorObj B C) (h : CategoryTheory.CategoryStruct.comp s₁ (CategoryTheory.CategoryStruct.comp (CategoryTheory.MonoidalCategoryStruct.whiskerRight s₂ C) (CategoryTheory.MonoidalCategoryStruct.associator A B C).hom) = CategoryTheory.CategoryStruct.comp s₃ (CategoryTheory.MonoidalCategoryStruct.whiskerLeft A s₄)) {V W Z : D} (m : A ⟶ CategoryTheory.MonoidalCategoryStruct.tensorObj R V) (n : B ⟶ CategoryTheory.MonoidalCategoryStruct.tensorObj R W) (p : C ⟶ CategoryTheory.MonoidalCategoryStruct.tensorObj R Z) :

Associativity of the shuffle at arbitrary sources. Given a coherence identity between the two ways of reassociating the chosen sources, the two ways of shuffling three morphisms agree.

theorem RS.freeModShuffle_assoc_at' {D : Type u} [CategoryTheory.Category.{v, u} D] [CategoryTheory.MonoidalCategory D] [CategoryTheory.BraidedCategory D] (R : D) [CategoryTheory.MonObj R] {A B C T T' T'' : D} (s₁ : T ⟶ CategoryTheory.MonoidalCategoryStruct.tensorObj T' C) (s₂ : T' ⟶ CategoryTheory.MonoidalCategoryStruct.tensorObj A B) (s₃ : T ⟶ CategoryTheory.MonoidalCategoryStruct.tensorObj A T'') (s₄ : T'' ⟶ CategoryTheory.MonoidalCategoryStruct.tensorObj B C) (h : CategoryTheory.CategoryStruct.comp s₁ (CategoryTheory.CategoryStruct.comp (CategoryTheory.MonoidalCategoryStruct.whiskerRight s₂ C) (CategoryTheory.MonoidalCategoryStruct.associator A B C).hom) = CategoryTheory.CategoryStruct.comp s₃ (CategoryTheory.MonoidalCategoryStruct.whiskerLeft A s₄)) {V W Z : D} (m : A ⟶ CategoryTheory.MonoidalCategoryStruct.tensorObj R V) (n : B ⟶ CategoryTheory.MonoidalCategoryStruct.tensorObj R W) (p : C ⟶ CategoryTheory.MonoidalCategoryStruct.tensorObj R Z) :

RS.freeModShuffle_assoc_at, bracketed as realization of the reassociation of the generators produces it.

The braiding on the four sources #

The four families of the unitor and the braiding #

The fibre functor and its comparison data #

Associativity #

Associativity of the monoidal comparison of the fibre functor: the two ways of comparing a threefold tensor product agree, up to the associator of the super modules and the reassociation of the three objects.

Unitality #

Compatibility with the braiding #

The monoidal comparison of the fibre functor commutes with the braiding: swapping the two factors of the super-module tensor product and comparing agrees with comparing and swapping the two objects. The Koszul sign of the odd-odd block of the Koszul swap is RS.freeModShuffle_braiding_oo, and it is again supplied by RS.oddLine_sq_inv_braiding.

The lax monoidal and lax braided structures #