
theorem
  for n being non zero Nat holds PrimeDivisors n c= Seg n
  proof
    let n be non zero Nat;
    let x be object;
    assume x in PrimeDivisors n;
    then consider k being Prime such that
A1: x = k and
A2: k divides n;
A3: 1 <= k by INT_2:def 4;
    k <= n by A2,INT_2:27;
    hence thesis by A1,A3;
  end;
