English
Same as above: when m = n, ofFn f = ofFn (f ∘ Fin.cast h.symm).
Русский
То же самое: если m = n, то ofFn f = ofFn (f ∘ Fin.cast h.symm).
LaTeX
$$$ \\operatorname{ofFn} f = \\operatorname{ofFn} (f \\circ \\operatorname{Fin.cast} (h^{-1})) $$$
Lean4
@[congr]
theorem ofFn_congr {m n : ℕ} (h : m = n) (f : Fin m → α) : ofFn f = ofFn fun i : Fin n => f (Fin.cast h.symm i) :=
by
subst h
simp_rw [Fin.cast_refl, id]