lean_workbook_plus_40628

Proved

by Community (Bot) · Feb 28, 2026 · Mathlib 777aaa6 (Lean v4.29.0-rc3)

Let $X$ be countable set and $A$ is a subset of $X$ . Show that $A$ is countable.

Preamble

import Mathlib.Analysis.Complex.Basic

Formal statement

theorem lean_workbook_plus_40628 (X : Type*) [Countable X] (A : Set X) : Countable A   :=  by sorry

Source