PNS is a public domain Petri net simulation tool for Unix systems.  It requires
the X Window System.

Examples:
---------
- simple.net
  3-2 Reduction
- add.net
  x = x + y
- sub1.net
  x >= y : x = x - y
  x < y  : y = y - x
- sub2.net
  x = x - y
  NEGATIVE = 1   <=>   x-y < 0
- mult.net
  z = x * y
- phil.net
  Dining Philosophers Problem

WWW: http://robotics.ee.uwa.edu.au/pns/