Let t be given.
Let y be given.
We prove the intermediate
claim Ht_eq:
t = y.
rewrite the current goal using Heq (from left to right).
Use reflexivity.
rewrite the current goal using Heq (from left to right).
Use reflexivity.
rewrite the current goal using Hz_eq (from left to right).
rewrite the current goal using Ht_eq (from right to left).
Use reflexivity.
∎