Changes by: Aleksey Nogin (nogin at cs.caltech.edu)
Date: 2006-02-12 21:06:24 -0800 (Sun, 12 Feb 2006)
Revision: 8671
Log message:

      Weakened the nilEquality axiom, replacing the 
      "type"{list{'A}} --> nil in list{'A}
      (which is a bit too srtong semantically) with weaker theorems of the form
      list{'A} --> list{'A}
      
      This was first added un rev 8660, but then reverted in rev 8670.