Let f and g be given.
Let n be given.
We prove the intermediate
claim HfnR:
apply_fun f n ∈ R.
We prove the intermediate
claim HgnR:
apply_fun g n ∈ R.
rewrite the current goal using Hdef1 (from left to right).
rewrite the current goal using Hdef2 (from left to right).
rewrite the current goal using Habs (from left to right).
Use reflexivity.
∎