Metamath Proof Explorer

Theorem conss1

Description: Contrapositive law for subsets. (Contributed by Andrew Salmon, 15-Jul-2011)

Ref Expression
Assertion conss1 
|- ( ( _V \ A ) C_ B <-> ( _V \ B ) C_ A )

Proof

Step Hyp Ref Expression
1 difcom 
 |-  ( ( _V \ A ) C_ B <-> ( _V \ B ) C_ A )