Description: A set if regularly open iff it is the interior of some closed set. (Contributed by Jeff Hankins, 27-Sep-2009)
Ref | Expression | ||
---|---|---|---|
Hypothesis | opnregcld.1 | |
|
Assertion | cldregopn | |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | opnregcld.1 | |
|
2 | 1 | clscld | |
3 | eqcom | |
|
4 | 3 | biimpi | |
5 | fveq2 | |
|
6 | 5 | rspceeqv | |
7 | 2 4 6 | syl2an | |
8 | 7 | ex | |
9 | cldrcl | |
|
10 | 1 | cldss | |
11 | 1 | ntrss2 | |
12 | 9 10 11 | syl2anc | |
13 | 1 | clsss2 | |
14 | 12 13 | mpdan | |
15 | 1 | ntrss | |
16 | 9 10 14 15 | syl3anc | |
17 | 1 | ntridm | |
18 | 9 10 17 | syl2anc | |
19 | 1 | ntrss3 | |
20 | 9 10 19 | syl2anc | |
21 | 1 | clsss3 | |
22 | 9 20 21 | syl2anc | |
23 | 1 | sscls | |
24 | 9 20 23 | syl2anc | |
25 | 1 | ntrss | |
26 | 9 22 24 25 | syl3anc | |
27 | 18 26 | eqsstrrd | |
28 | 16 27 | eqssd | |
29 | 28 | adantl | |
30 | 2fveq3 | |
|
31 | id | |
|
32 | 30 31 | eqeq12d | |
33 | 29 32 | syl5ibrcom | |
34 | 33 | rexlimdva | |
35 | 8 34 | impbid | |