| context | ${\bf C}$ … category |
| definiendum | ${\bf C}^\mathrm{op}$ |
| definition | $\mathrm{Ob}_{{\bf C}^\mathrm{op}}:=\mathrm{Ob}_{\bf C} $ |
| definition | ${\bf C}^\mathrm{op}[A,B]:={\bf C}[B,A]$ |
| definition | $f\,\circ_{{\bf C}^\mathrm{op}}\,g\ :=\ g\,\circ_{{\bf C}}\,f$ |
Wikipedia: Opposite category