Metamath Proof Explorer


Theorem ioossre

Description: An open interval is a set of reals. (Contributed by NM, 31-May-2007)

Ref Expression
Assertion ioossre
|- ( A (,) B ) C_ RR

Proof

Step Hyp Ref Expression
1 elioore
 |-  ( x e. ( A (,) B ) -> x e. RR )
2 1 ssriv
 |-  ( A (,) B ) C_ RR