Theorem rel0

Description: The empty set is a relation. (Contributed by NM, 26-Apr-1998)

	Ref	Expression
Assertion	rel0	|- Rel (/)

Proof

Step	Hyp	Ref	Expression
1		0ss	|- (/) C_ ( _V X. _V )
2		df-rel	|- ( Rel (/) <-> (/) C_ ( _V X. _V ) )
3	1 2	mpbir	|- Rel (/)