SYS V/ULTRIX compatability

[rachiele at nadc.arpa]

I need information on the compatability/incompatability between software
written on UNIX System V and ULTRIX.  Mainly, what type of things will not
work when you try to port software?  What does the PROG_ENV environment
variable give you?  How can you write software which will run on both
systems?

   Please respond to rachiele at nadc.arpa.
    Thank you.
       Jim Rachiele