English
The product R × S is a StarModule over α with star_smul defined componentwise: star_smul(a, (r,s)) = (star a · star r, star a · star s).
Русский
Произведение R × S является StarModule над α с определением star_smul по компонентам: star_smul(a, (r,s)) = (star a · star r, star a · star s).
LaTeX
$$$\\\\star_smul(a, (r,s)) = (\\\\star a \\\\cdot \\\\star r, \\\\star a \\\\cdot \\\\star s).$$$
Lean4
instance {α : Type w} [SMul α R] [SMul α S] [Star α] [Star R] [Star S] [StarModule α R] [StarModule α S] :
StarModule α (R × S) where star_smul _ _ := Prod.ext (star_smul _ _) (star_smul _ _)