English
For any a in ZMod n, the first projection of its cast to R × S equals the cast: (cast a : R × S).fst = cast a.
Русский
Для любого a ∈ ZMod n, первая компонента приведения в R × S совпадает с привидением: (cast a : R × S).fst = cast a.
LaTeX
$$$ (\operatorname{cast} a : R \times S).\mathrm{fst} = \operatorname{cast} a $$$
Lean4
@[simp]
theorem _root_.Prod.fst_zmod_cast (a : ZMod n) : (cast a : R × S).fst = cast a :=
by
cases n
· rfl
· simp [ZMod.cast]