Lean4
/-- Semigroup homomorphism between the function spaces `I → α` and `I → β`, induced by a semigroup
homomorphism `f` between `α` and `β`. -/
@[to_additive (attr := simps) /-- Additive semigroup homomorphism between the function spaces
`I → α` and `I → β`, induced by an additive semigroup homomorphism `f` between `α` and `β` -/
]
protected def compLeft {α β : Type*} [Mul α] [Mul β] (f : α →ₙ* β) (I : Type*) : (I → α) →ₙ* I → β
where
toFun h := f ∘ h
map_mul' _ _ := by ext; simp