Intuitionize snprc in iset.mm
Intuitionize snprc in iset.mm

The statement of the theorem does not change, and the proof is
similar in the sense of relying on elsn and isset. However,
the logic needs reorganization including changing neq0 to
eq0 and generally different handling of negation.

metamath/set.mm,metamath/set.mm,metamath/set.mm