Metamath Proof Explorer

Theorem ssct

Description: Any subset of a countable set is countable. (Contributed by Thierry Arnoux, 31-Jan-2017) Avoid ax-pow , ax-un . (Revised by BTernaryTau, 7-Dec-2024)

Ref Expression
Assertion ssct 
|- ( ( A C_ B /\ B ~<_ _om ) -> A ~<_ _om )

Proof

Step Hyp Ref Expression
1 domssl 
 |-  ( ( A C_ B /\ B ~<_ _om ) -> A ~<_ _om )