Books on portability between Unixes?

[Jorge Gautier]

In article <1991May20.174803.15870 at kong.gsfc.nasa.gov> njacobs at kong.gsfc.nasa.gov (Nick Jacobs - EOS) writes:
>In article <1991May9.181650.12516 at homecare.COM> jessea at homecare.COM (Jesse W. Asher) writes:
>>I'd like to write some software that is very portable between different
>>types of Unix.  I'm not just talking about BSD vs. SystemV, but also how
>>   [...etc]
> Get the XPG manuals from X/Open. Use them as programmer's reference
> manuals.

How can these manuals be obtained?  Bookstores, mail order, ?  I would
appreciate a pointer.  Thanks.
--
Jorge A. Gautier| "The enemy is at the gate.  And the enemy is the human mind
jgautier at ads.com|  itself--or lack of it--on this planet."  -General Boy
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