theorem Th37:
  c in SetImp A iff ex p,q st c = p` "\/" q & p in A & q in A
proof
  hereby
    assume c in SetImp A;
    then consider p,q such that
A1: c = p => q & p in A & q in A;
    take p,q;
    thus c = p` "\/" q & p in A & q in A by A1,FILTER_0:42;
  end;
  given p,q such that
A2: c = p` "\/" q and
A3: p in A & q in A;
  c = p => q by A2,FILTER_0:42;
  hence thesis by A3;
end;
