Let x0 of type ι be given.
Let x1 of type ι → ι → ι be given.
Let x2 of type ι be given.
Assume H1: x2 ∈ x0.
Apply explicit_Group_identity_prop with
x0,
x1,
x1 (explicit_Group_identity x0 x1) x2 = x2 leaving 2 subgoals.
The subproof is completed by applying H0.