English
If each αi carries a MulAction M on αi, then the Pi-type ∀i αi carries a MulAction M defined pointwise by (m • f)(i) = m • f(i).
Русский
Пусть на каждом αi задано действие MulAction M. Тогда на ∀i αi будет естественно задано действие M по координатам: (m • f)(i) = m • f(i).
LaTeX
$$$\text{MulAction } M\big(\forall i\, \alpha_i\big)\text{ with } (m\cdot f)(i) = m\cdot f(i).$$$
Lean4
@[to_additive]
instance mulAction (M) {m : Monoid M} [∀ i, MulAction M (α i)] : @MulAction M (∀ i, α i) m
where
smul := (· • ·)
mul_smul _ _ _ := funext fun _ ↦ mul_smul _ _ _
one_smul _ := funext fun _ ↦ one_smul _ _