Convert between versions of UNIX

[John R. Brinkema]

I am writing a paper about the problems of converting (porting) software
between various versions of UNIX, in particular *standard UNIX* System V,
BSD 4.x, and Xenix.  I have done many ports in many 'directions' but am
very interested in others' experience.

In particular, do you have a standard procedure; a set of feature-areas that
you always check; tricks that make the porting easier?  Also what are the
hardest feature to port; what features are so subtle that bugs from them
hide?

I will sumarize.  tia.  jb.