
theorem Th1:
  for i1 being Nat st 1 <= i1 holds i1-'1<i1
proof
  let i1 be Nat;
  assume
A1: 1 <= i1;
  i1 - 1 < i1 - 0 by XREAL_1:15;
  hence thesis by A1,XREAL_1:233;
end;
