Remark [efr-J0WW]

For any monoidal category \mathcal {C}, \mathsf {Optic}_\mathcal {C}\left ({A \choose X}, {I \choose I}\right ) = \mathcal {C}(X,A). One way to think of an optic {A \choose X} \leftrightarrows {B \choose Y} is as a string diagram X \to A, but which has a hole with space for a morphism B \to Y. One inserts such a morphism by composing the optic with the optic {B \choose Y} \leftrightarrows {I \choose I} representing it. This idea of "open diagrams" has been developed in much more detail by Román, Reference [roman-optics-coend].