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.
freeModShuffle_assoc: associativity, against the reassociation of the generators.freeModShuffle_unit_left: filling the first algebra slot with the unit leaves the left action of the free module.freeModShuffle_unit_right: filling the second algebra slot with the unit leaves the braided right action of the free module.freeModShuffle_braiding: the shuffle commutes with the braiding.
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 #
Two multiplications, with a reassociation of the generators carried past them.
Two multiplications, with a reassociation of the generators carried past them.
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.
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 #
Interchanging against a leading unit is a reassociation.
Interchanging against a leading unit is a reassociation.
Left unitality of the shuffle: filling the first generator slot with the unit turns the shuffle into the left action of the free module, written out.
Left unitality of the shuffle: filling the first generator slot with the unit turns the shuffle into the left action of the free module, written out.
Interchanging against a trailing unit is the slide.
Interchanging against a trailing unit is the slide.
Right unitality of the shuffle: filling the second generator slot with the unit turns the shuffle into the braided right action of the free module, written out.
Right unitality of the shuffle: filling the second generator slot with the unit turns the shuffle into the braided right action of the free module, written out.
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.
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.