theorem Th12:
  <*{},f,p*> in SFHTs(D)
  proof
A1: {} is PartialPredicate of D by RELSET_1:12;
    for d holds d in dom {} & {}.d = TRUE & d in dom f & f.d in dom p
     implies p.(f.d) = TRUE;
    hence thesis by A1;
end;
