English
Multiplicativity of cast: (cast (a * b : ZMod n) : R) = cast a * cast b.
Русский
Умножение сохраняется: cast(a*b) = cast a * cast b.
LaTeX
$$$\\\\forall {n : \\\\mathbb{N}} {R : Type*} [Ring R] [CharP R n] (a b : ZMod n), \\\\operatorname{cast} (a * b) = \\\\operatorname{cast} a \\\\cdot \\\\operatorname{cast} b$$$
Lean4
theorem cast_mul' (a b : ZMod n) : (cast (a * b : ZMod n) : R) = cast a * cast b := by simp