Alphabeta Math
DefinitionDefinition: Literature-sourcedProof: Not applicablePipeline-generatedjudge pass (gpt-6.1-sol)
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Local Yang–Baxter operators on tensor powers

Definition

Let C be a monoidal category, let X∈C, let R be a Yang–Baxter operator on X (Yang–Baxter operators on an object), and let n≥2. Write X⊗n for the left-nested tensor power: X⊗0:=1, X⊗1:=X and X⊗(k+1):=X⊗k⊗X for k≥1; write 1X⊗k for the k-fold tensor power of id⁡X.

Work first in a strict model C′ of C, obtained from a monoidal equivalence as in Mac Lane strictification, and let R′ ⁣:X′⊗X′→X′⊗X′ be the transported Yang–Baxter operator. The local Yang–Baxter operators are the automorphisms of the n-fold tensor power

Ri:=1X⊗(i−1)⊗R⊗1X⊗(n−i−1)∈Aut⁡C(X⊗n),1≤i≤n−1,

where in the strict model the display is literal and each Ri is the endomorphism of X′⊗n acting as R′ on the i-th and (i+1)-st tensor factors and as the identity elsewhere.

Outside the strict model the same operators are obtained by conjugating the displayed word with canonical associativity isomorphisms: the composite

X⊗n→ κ X⊗(i−1)⊗(X⊗X)⊗X⊗(n−i−1)→ 1⊗(i−1)⊗R⊗1⊗(n−i−1) X⊗(i−1)⊗(X⊗X)⊗X⊗(n−i−1)→ κ−1 X⊗n,

where κ is any canonical morphism between the two parenthesised tensor words built from associators and unitors, is independent of the chosen κ by Mac Lane coherence in canonical-map form (Mac Lane coherence in canonical-map form), and it is this composite that defines Ri in C.

Each Ri is invertible, with inverse 1X⊗(i−1)⊗R−1⊗1X⊗(n−i−1) (respectively its bracket-corrected conjugate): the displayed inverse is a two-sided inverse of the displayed word in the strict model, and conjugation by κ preserves the inverse relation.

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