theorem nfmax {x: nat} (a b: nat x):
  $ FN/ x a $ >
  $ FN/ x b $ >
  $ FN/ x max a b $;
    | Step | Hyp | Ref | Expression | 
|---|---|---|---|
| 1 | anl | u = a /\ v = b -> u = a | |
| 2 | anr | u = a /\ v = b -> v = b | |
| 3 | 1, 2 | maxeqd | u = a /\ v = b -> max u v = max a b | 
| 4 | hyp h1 | FN/ x a | |
| 5 | hyp h2 | FN/ x b | |
| 6 | 3, 4, 5 | nfnlem2 | FN/ x max a b |