The natural transformation \(\sigma _{XY}\) and \(\tau _{XY}\) that are the components of the natural isomorphism in the adjunction \(\mathscr {L} \dashv \mathscr {R} : {\cal C} \rightleftarrows {\cal D}\) are related to the unit and counit of the adjunction: \[\begin {aligned} \sigma _{XY}(f) & = \eta _X \mathbin {\bullet } \mathscr {R}(f^{\sharp })\\ \tau _{XY}(g) & = \mathscr {L}(g^{\flat }) \mathbin {\bullet } \epsilon _Y \end {aligned} \] and they are reverse of each other \[\sigma _{XY} = \tau _{YX}^{-1}\]