English
If two group homomorphisms f1 and f2 are equal, then any construction F that depends functorially on f1 is equal to the corresponding construction on f2 after transporting along the equality.
Русский
Если два гомоморфизма f1 и f2 равны, то любая конструкция F, зависящая функториально от f, равна соответствующей конструкций, перенесённой по равенству.
LaTeX
$$$$ F(f_1,\\phi) = F(f_2, h\\,\\triangleright\\,\\phi) \\quad \\text{when } f_1=f_2. $$$$
Lean4
@[elab_as_elim]
theorem groupCohomology_induction_on [Group G] {A : Rep k G} {n : ℕ} {C : groupCohomology A n → Prop}
(x : groupCohomology A n) (h : ∀ x : cocycles A n, C (π A n x)) : C x :=
by
rcases (ModuleCat.epi_iff_surjective (π A n)).1 inferInstance x with ⟨y, rfl⟩
exact h y