Let x, y and z be given.
rewrite the current goal using HdefD (from left to right).
Use reflexivity.
rewrite the current goal using HdefD (from left to right).
Use reflexivity.
rewrite the current goal using HdefD (from left to right).
Use reflexivity.
rewrite the current goal using Happxy (from right to left) at position 1.
rewrite the current goal using Happyz (from right to left) at position 1.
rewrite the current goal using Happxz (from right to left) at position 1.
An exact proof term for the current goal is HtriD.
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