Subset_of_Countably_Infinite_Set_is_Countable
Provedcountable-setsproofwikisubsets
Every subset of a countably infinite set is countable.
Preamble
import Mathlib.Analysis.Complex.Basic
Formal statement
theorem Subset_of_Countably_Infinite_Set_is_Countable (S : Set ℕ) : Set.Countable S := by sorry
Source