Q:\DIF\DIF.TXT           2000 August 16

The function DIF takes the pair(x,y) to the relative complement
intersection(x,complement(y)).  Using the GOEDEL program, we have
found some ideas for defining this function.  The prettiest formula
found is this:

equal(composite(VERTSECT(intersection(composite(inverse(E),FIRST),
      composite(complement(inverse(E)),SECOND))),id(cart(V,V))),DIF).

See the notebook G:\2000\AUG\16\SYMDIF.NB.