Let x be given.
Apply (Hcharts x HxX) to the current goal.
Let U be given.
Apply HexV to the current goal.
Let V be given.
Apply Hexf to the current goal.
Let f be given.
We prove the intermediate
claim HopenU:
open_in X Tx U.
We prove the intermediate
claim HUinTx:
U ∈ Tx.
An
exact proof term for the current goal is
(open_in_elem X Tx U HopenU).
We prove the intermediate
claim HxU:
x ∈ U.
We use U to witness the existential quantifier.
Apply andI to the current goal.
Apply andI to the current goal.
An exact proof term for the current goal is HUinTx.
An exact proof term for the current goal is HxU.
We use V to witness the existential quantifier.
Apply andI to the current goal.
An exact proof term for the current goal is HVinTe.
We use f to witness the existential quantifier.
An exact proof term for the current goal is Hhomeo.
∎