The twist-shuffle coherence #
The pure braid identity of the twist shuffle: routing the scalar out of the first twisted factor, through the interchange, and back into the middle equals associating it into the second factor and interchanging. Two crossings cancel by symmetry.
The twist-shuffle coherence: extracting A from the twisted
factor V ⊗ R, interchanging, and reinserting it between R and
S agrees with associating A into W ⊗ S and interchanging.
The block braiding β_ (V ⊗ R) A contributes crossings of A past
R and past V; the latter cancels against β_ A V by symmetry,
the former is conjugated through the interchange block by
naturality of the braiding and cancels against (β_ R A).inv, and
the residual word is the interchange of V ⊗ R with
W ⊗ (A ⊗ S).
The twist-shuffle coherence: extracting A from the twisted
factor V ⊗ R, interchanging, and reinserting it between R and
S agrees with associating A into W ⊗ S and interchanging.
The block braiding β_ (V ⊗ R) A contributes crossings of A past
R and past V; the latter cancels against β_ A V by symmetry,
the former is conjugated through the interchange block by
naturality of the braiding and cancels against (β_ R A).inv, and
the residual word is the interchange of V ⊗ R with
W ⊗ (A ⊗ S).
The twist-act coherence: extracting A from the twisted factor
V ⊗ R before the interchange agrees with interchanging first and
then extracting A from the product V ⊗ W. Both words consist
of the crossings of A past V, of R past W, and of A past
W, each occurring exactly once; the two sides differ only in the
order of the first two, which act on disjoint factors and are
exchanged as whiskerings.
The twist-act coherence: extracting A from the twisted factor
V ⊗ R before the interchange agrees with interchanging first and
then extracting A from the product V ⊗ W. Both words consist
of the crossings of A past V, of R past W, and of A past
W, each occurring exactly once; the two sides differ only in the
order of the first two, which act on disjoint factors and are
exchanged as whiskerings.