English
Adding two fractions in the localization by the same denominator yields the sum with the common denominator.
Русский
Сложение двух дробей в локализации с одинаковым знаменателем даёт сумму с этим знаменателем.
LaTeX
$$$$ \\mathrm{mk} a b + \\mathrm{mk} c b = \\mathrm{mk}(a + c) b $$$$
Lean4
theorem add_mk (a b c d) : (mk a b : Localization M) + mk c d = mk ((b : R) * c + (d : R) * a) (b * d) :=
by
rw [add_comm (b * c) (d * a), mul_comm b d]
exact OreLocalization.oreDiv_add_oreDiv