Let X, Y, d, fn and f be given.
Let x be given.
Let eps be given.
Apply (Hunif eps HepsR HepsPos) to the current goal.
Let N be given.
We use N to witness the existential quantifier.
Apply andI to the current goal.
Let n be given.
An exact proof term for the current goal is (Htail n HnO HNn x HxX).
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