Update cbval2 and related theorems in iset.mm
Update cbval2 and related theorems in iset.mm

This is cbval2 , cbvex2 , cbval2v , and cbvex2v .
The replacements are copied verbatim from set.mm and verify
as-is.  The changes are primarily using F/ .

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