English
The closure of a set is dense if and only if the set itself is dense: Dense(closure s) ↔ Dense(s).
Русский
Замыкание множества плотно тогда, когда само множество плотно: Dense(closure s) ↔ Dense(s).
LaTeX
$$$\\\\text{Dense}(closure(s)) \\\\iff \\\\text{Dense}(s)$$$
Lean4
/-- The closure of a set `s` is dense if and only if `s` is dense. -/
@[simp]
theorem dense_closure : Dense (closure s) ↔ Dense s := by rw [Dense, Dense, closure_closure]