Documentation

LeanPool.RegtsSevenster.RS.Classical.Deligne.FreeModShuffleCoh

Coherence of the free-module shuffle #

The shuffle freeModShuffle R V W : (R ⊗ V) ⊗ (R ⊗ W) ⟶ R ⊗ (V ⊗ W) of RS.freeModTensor obeys the coherence of a monoidal structure. The four identities recorded here are pure identities of the ambient braided monoidal category: no coequalizer and no module theory appears in any of them, and everything is stated in raw R ⊗ V language.

The first two need only a monoid R; the third needs R commutative. The fourth needs the ambient braiding to be a symmetry: the two legs differ, in a merely braided category, by the double twist of the leading algebra factor past the second generator, and that double twist is not the identity. Accordingly freeModShuffle_braiding is stated over a SymmetricCategory, as is the interchange identity RS.tensorμ_braiding behind it.

Associativity #

Associativity of the shuffle: shuffling the first two free modules and then the third agrees, up to the reassociation of the generators, with shuffling the last two and then the first.

Unitality #

Compatibility with the braiding #

The shuffle commutes with the braiding: swapping the two free modules and shuffling agrees with shuffling and swapping the two generators. Commutativity of R swaps the algebra factors; the symmetry of the ambient braiding untwists the generators.