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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