English
Let f: Fin(n+1) → M. For i ∈ Fin(n+1), partialProd( init f ) i equals partialProd f i.castSucc.
Русский
Пусть f: Fin(n+1) → M. Тогда partialProd( init f ) i = partialProd f( i.castSucc ).
LaTeX
$$$$\\text{partialProd}(\\text{init } f, i) = \\text{partialProd}(f, i^{\\mathrm{castSucc}}).$$$$
Lean4
@[to_additive]
theorem partialProd_init {f : Fin (n + 1) → M} (i : Fin (n + 1)) : partialProd (init f) i = partialProd f i.castSucc :=
i.inductionOn (by simp) fun i hi => by simp_all [init, partialProd_succ]