
theorem Th1:
  for n being non zero Nat holds n <> 1 implies n >= 2
proof
  let n be non zero Nat;
  assume
A1: n <> 1;
  assume n < 2;
  then n < 1 + 1;
  then n <= 0 + 1 by NAT_1:13;
  hence contradiction by A1,NAT_1:8;
end;
