It is a general rule of the Diagram Macros that to draw an arrow in some given direction, it suffices to preceed the name of the arrow by a code for the direction. To draw an in-text arrow in the backward direction, it suffices to add the prefix +bk+ to the command for that arrow.
| backward plain arrow | ++ | |
| backward dotted arrow | ++ | |
| backward monomorphism | ++ | |
| backward epimorphism | ++ | |
| backward bimorphism | ++ | |
| backward isomorphism | ++ | |
| backward pair of parallel arrows | ++ | |
| backward equality | ++ | |
| backward pair of adjoint arrows | ++ |