English
If m and k are coprime and n and k are coprime, then m n and k are coprime.
Русский
Если m и k взаимно просты, и n и k взаимно просты, то mn и k взаимно просты.
LaTeX
$$$ m.Coprime k \\rightarrow n.Coprime k \\rightarrow (m \\cdot n).Coprime k $$$
Lean4
theorem mul {k m n : ℕ+} : m.Coprime k → n.Coprime k → (m * n).Coprime k :=
by
repeat rw [← coprime_coe]
rw [mul_coe]
apply Nat.Coprime.mul_left