reserve i,j,k,n for Nat;
reserve x,x1,x2,x3,y1,y2,y3 for set;

theorem Th3:
  for x be non zero Nat holds 0 in x
proof
  let x be non zero Nat;
  reconsider n = x as Element of NAT by ORDINAL1:def 12;
  n = {i where i is Nat: i < n} & 0 < n by AXIOMS:4;
  hence thesis;
end;
