theorem Th46:
  for f being set st f in PFuncs(X,Y) holds f is PartFunc of X,Y
proof
  let f be set;
  assume f in PFuncs(X,Y);
  then ex F being Function st f = F & dom F c= X & rng F c= Y by Def3;
  hence thesis by RELSET_1:4;
end;
