Description: The successor of a successor ordinal number is a compact topology, proven without the Axiom of Regularity. (Contributed by Chen-Pang He, 18-Oct-2015)
Ref | Expression | ||
---|---|---|---|
Hypothesis | onsucsuccmpi.1 | |
|
Assertion | onsucsuccmpi | |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | onsucsuccmpi.1 | |
|
2 | 1 | onsuci | |
3 | onsuctop | |
|
4 | 2 3 | ax-mp | |
5 | 1 | onirri | |
6 | 1 1 | onsucssi | |
7 | 5 6 | mtbi | |
8 | sseq1 | |
|
9 | 7 8 | mtbii | |
10 | elpwi | |
|
11 | 10 | unissd | |
12 | 1 | onunisuci | |
13 | 11 12 | sseqtrdi | |
14 | 9 13 | nsyl | |
15 | eldif | |
|
16 | elpwunsn | |
|
17 | 15 16 | sylbir | |
18 | 17 | ex | |
19 | df-suc | |
|
20 | 19 | pweqi | |
21 | 18 20 | eleq2s | |
22 | snelpwi | |
|
23 | snfi | |
|
24 | 23 | jctr | |
25 | elin | |
|
26 | 24 25 | sylibr | |
27 | 2 | elexi | |
28 | 27 | unisn | |
29 | 28 | eqcomi | |
30 | unieq | |
|
31 | 30 | rspceeqv | |
32 | 26 29 31 | sylancl | |
33 | 22 32 | syl | |
34 | 14 21 33 | syl56 | |
35 | 34 | rgen | |
36 | 2 | onunisuci | |
37 | 36 | eqcomi | |
38 | 37 | iscmp | |
39 | 4 35 38 | mpbir2an | |