This is a package of commutative diagram macros built on top of Xy-pic  by Michael Barr (email: barr@barrs.org). Its use is unrestricted. It  may be freely distributed, unchanged, for non-commercial or commercial  use. If changed, it must be renamed. Inclusion in a commercial  software package is also permitted, but I would appreciate receiving a  free copy for my personal examination and use. There are no guarantees  that this package is good for anything. I have tested it with LaTeX 2e,  LaTeX 2.09 and Plain TeX. Although I know of no reason it will not work  with AMSTeX, I have not tested it.