reserve x, y, z, E, E1, E2, E3 for set,
  sE for Subset-Family of E,
  f for Function of E, E,
  k, l, m, n for Nat;

theorem Th2:
  for S being non empty Subset of NAT st 0 in S holds min S = 0
by XXREAL_2:def 7;
