reserve A for set, x,y,z for object,
  k for Element of NAT;
reserve n for Nat,
  x for object;
reserve V, C for set;

theorem Th59:
  for X being set, f being Function of X, NAT holds f in NatMinor f
proof
  let X be set, f be Function of X, NAT;
  for x being set st x in X holds f.x <= f.x;
  hence thesis by Def14;
end;
