reserve i, j, k, l, m, n, t for Nat;

theorem
  for k be non trivial Nat holds k >= 2
proof
  let k be non trivial Nat;
  k >= 1 by NAT_1:14;
  then k > 1 or k = 1 by XXREAL_0:1;
  then k >= 1 + 1 by Def1,NAT_1:13;
  hence thesis;
end;
