Let x be given.
Assume Hx.
Let x' be given.
Assume Hx'.
We will prove lam_comp X' g f (bX x x') = bZ ((λx ∈ X' ⇒ g (f x)) x) ((λx ∈ X' ⇒ g (f x)) x').
rewrite the current goal using beta X' (λx ⇒ g (f x)) x Hx (from left to right).
rewrite the current goal using beta X' (λx ⇒ g (f x)) x' Hx' (from left to right).
We will prove (λx ∈ X' ⇒ g (f x)) (bX x x') = bZ (g (f x)) (g (f x')).
rewrite the current goal using beta X' (λx ⇒ g (f x)) (bX x x') (HbX x Hx x' Hx') (from left to right).
We will prove g (f (bX x x')) = bZ (g (f x)) (g (f x')).
rewrite the current goal using Hg2 (f x) (ap_Pi X' (λ_ ⇒ Y') f x Hf1 Hx) (f x') (ap_Pi X' (λ_ ⇒ Y') f x' Hf1 Hx') (from right to left).
We will prove g (f (bX x x')) = g (bY (f x) (f x')).
Use f_equal.
An exact proof term for the current goal is Hf2 x Hx x' Hx'.