
theorem
  for t1, t2 being t-norm st t1 <= t2 holds
    conorm t2 <= conorm t1
  proof
    let t1, t2 be t-norm;
    set c1 = conorm t1, c2 = conorm t2;
    assume
A1: t1 <= t2;
    for a,b being Element of [.0,1.] holds
      c2.(a,b) <= c1.(a,b)
    proof
      let a,b be Element of [.0,1.];
      1-a in [.0,1.] & 1-b in [.0,1.] by OpIn01; then
      1 - t2.(1-a,1-b) <= 1 - t1.(1-a,1-b) by A1,XREAL_1:10; then
      1 - t2.(1-a,1-b) <= c1.(a,b) by CoDef;
      hence thesis by CoDef;
    end;
    hence thesis;
  end;
