theorem
  for a be non trivial Nat, p be prime Nat st p > a holds
    not p divides a & not a divides p
  proof
    let a be non trivial Nat, p be prime Nat;
    assume p > a; then
    a,p are_coprime by NAT_6:6,NAT_D:7;
    hence thesis by NTC;
  end;
