Let w and u be given.
We will
prove Inj0 u ∈ w.
Let z be given.
Apply H3 to the current goal.
Let x be given.
We will
prove Inj0 u ∈ w.
rewrite the current goal using H4 (from left to right).
rewrite the current goal using H5 (from right to left).
rewrite the current goal using
Unj_Inj0_eq (from left to right).
We will
prove Inj0 x ∈ w.
rewrite the current goal using H5 (from left to right).
An exact proof term for the current goal is H2.
∎