Description: The set of open intervals with rational endpoints forms a basis for a topology. (Contributed by NM, 8-Mar-2007)
Ref | Expression | ||
---|---|---|---|
Assertion | qtopbas | |- ( (,) " ( QQ X. QQ ) ) e. TopBases |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | qssre | |- QQ C_ RR |
|
2 | ressxr | |- RR C_ RR* |
|
3 | 1 2 | sstri | |- QQ C_ RR* |
4 | 3 | qtopbaslem | |- ( (,) " ( QQ X. QQ ) ) e. TopBases |