Theorem opprdomn

Description: The opposite of a domain is also a domain. (Contributed by Mario Carneiro, 15-Jun-2015)

	Ref	Expression
Hypothesis	opprdomn.1	|- O = ( oppR ` R )
Assertion	opprdomn	|- ( R e. Domn -> O e. Domn )

Proof

Step	Hyp	Ref	Expression
1		opprdomn.1	|- O = ( oppR ` R )
2	1	opprdomnb	|- ( R e. Domn <-> O e. Domn )
3	2	biimpi	|- ( R e. Domn -> O e. Domn )