English
IsRegular r iff both left and right regularity hold: ∀ x, r x = 0 ⇒ x = 0 and ∀ x, x r = 0 ⇒ x = 0.
Русский
IsRegular r эквивалентно тому, что и слева и справа регулярность выполняются: ∀ x, r x = 0 ⇒ x = 0 и ∀ x, x r = 0 ⇒ x = 0.
LaTeX
$$$\text{IsRegular}(r) \iff \Big(\forall x, r x = 0 \Rightarrow x = 0\Big) \land \Big(\forall x, x r = 0 \Rightarrow x = 0\Big)$$$
Lean4
theorem isRegular_iff_eq_zero_of_mul : IsRegular r ↔ (∀ x, r * x = 0 → x = 0) ∧ (∀ x, x * r = 0 → x = 0) := by
rw [isRegular_iff, isLeftRegular_iff_right_eq_zero_of_mul, isRightRegular_iff_left_eq_zero_of_mul]