
theorem
  for a,b be odd square Nat st a,b are_coprime holds not 3 divides (a + b)/2
  proof
    let a,b be odd square Nat such that
    A1: a,b are_coprime;
    (a + b)/2*2 = a + b; then
    (a + b)/2 divides a + b;
    hence thesis by A1,N02193,INT_2:9;
  end;
