English
The product of rationals q and r equals mkRat of the product of numerators and denominators.
Русский
Произведение рациональных чисел q и r равно mkRat( q.num · r.num, q.den · r.den ).
LaTeX
$$$ \forall q,r \in \mathbb{Q}, q r = mkRat (q.num \cdot r.num) (q.den \cdot r.den) $$$
Lean4
theorem mul_eq_mkRat (q r : ℚ) : q * r = mkRat (q.num * r.num) (q.den * r.den) := by rw [mul_def, normalize_eq_mkRat]