What is a pic

[Curtis Generous]

gwyn at smoke.BRL.MIL (Doug Gwyn) writes:
>"pic" is one of a set of troff preprocessors that interpret "small languages"
>for specialized purposes, in this case for diagram drawing.  Others include
>"eqn" for conveniently specifying mathematical equations, "tbl" for tables,
>and "grap" for convenient production of graphs.  ...

I have recently come across one troff preprocessor which I had never heard 
of before: grn.  It is used in the /usr/doc/ps1/07.ipctut documents on my
BSD machine, yet not available anywhere that I can find.  Any troff-gurus 
know what this 'grn' does, and where it can be obtained?

--curtis
-- 
Curtis C. Generous
Defense Technical Information Center (DTIC)
ARPA: generous at dev.dtic.dla.mil
UUCP: {uunet,vrdxhq}!dev!generous