I've yet to investigate, since nodes it's a bit advanced topic on PSTricks (latex package to do postcript drawings on LaTeX). I've used pstricks before, check "OrthogoncalCurves" entry for an example. I?ll tell you later what I find
f
G -----> H G
p \ /_ ----- ~ f(G)
\ / f ker f
G/ker f |
|
![[parent]](http://images.planetmath.org:8080/images/uparrow.png)