Metamath Proof Explorer

Theorem onssno

Description: The surreal ordinals are a subclass of the surreals. (Contributed by Scott Fenton, 18-Mar-2025)

Ref Expression
Assertion onssno 
|- On_s C_ No

Proof

Step Hyp Ref Expression
1 df-ons 
 |-  On_s = { x e. No | ( _Right ` x ) = (/) }
2 ssrab2 
 |-  { x e. No | ( _Right ` x ) = (/) } C_ No
3 1 2 eqsstri 
 |-  On_s C_ No