[Xy-pic] pullback symbols

Andrej Bauer Andrej.Bauer@andrej.com
30 Jul 2001 15:49:12 +0200

Don MacInnes <macinndx@cs.man.ac.uk> writes:
> I'm hoping someone can help by telling me how to draw the little
> `right-angle' device often used to show that a certain commuting square is
> a pullback/pushout using xypic.

I have this in my macros.tex and I do not know where I got it from
(neither do I understand what precisely it does):


Example of use:

              A \ar[r] \ar[d] \pullbackcorner  & B \ar[d] \\
              C \ar[r]                         & D \pushoutcorner