In mathematics, a commutativity constraint γ {\displaystyle \gamma } on a monoidal category C {\displaystyle {\mathcal {C}}} is a choice of isomorphism γ A, B : A ⊗ B → B ⊗ A {\displaystyle \gamma _{A,B}:A\otimes B\rightarrow B\otimes A} for each pair of objects A and B which form a "natural family." Wikipedia