Let p be given.
Apply Hexn to the current goal.
Let n be given.
Assume Hnpack.
Apply Hnpack to the current goal.
Assume HnIn Hpeq.
rewrite the current goal using Hpeq (from left to right).
rewrite the current goal using HflipEq (from right to left).
An exact proof term for the current goal is HflipI.
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