Let J, f, g and a be given.
Let j be given.
rewrite the current goal using Haj (from left to right).
An exact proof term for the current goal is (Hfcoords j HjJ).
We prove the intermediate
claim HfjR:
apply_fun f j ∈ R.
An exact proof term for the current goal is HfjSet.
An exact proof term for the current goal is (Hgcoords j HjJ).
We prove the intermediate
claim HgjR:
apply_fun g j ∈ R.
An exact proof term for the current goal is HgjSet.
∎