Metamath Proof Explorer

Theorem 0ss

Description: The null set is a subset of any class. Part of Exercise 1 of TakeutiZaring p. 22. (Contributed by NM, 21-Jun-1993)

Ref Expression
Assertion 0ss 
|- (/) C_ A

Proof

Step Hyp Ref Expression
1 noel 
 |-  -. x e. (/)
2 1 pm2.21i 
 |-  ( x e. (/) -> x e. A )
3 2 ssriv 
 |-  (/) C_ A