Description: Relationship involving membership, subset, and union. Exercise 5 of Enderton p. 26 and its converse. (Contributed by NM, 20-Sep-2003) Avoid ax-11 . (Revised by BTernaryTau, 28-Dec-2024)
Ref | Expression | ||
---|---|---|---|
Assertion | unissb | |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | eluni | |
|
2 | 1 | imbi1i | |
3 | 19.23v | |
|
4 | 2 3 | bitr4i | |
5 | 4 | albii | |
6 | elequ1 | |
|
7 | 6 | anbi1d | |
8 | eleq1w | |
|
9 | 7 8 | imbi12d | |
10 | elequ2 | |
|
11 | eleq1w | |
|
12 | 10 11 | anbi12d | |
13 | 12 | imbi1d | |
14 | 9 13 | alcomw | |
15 | 19.21v | |
|
16 | impexp | |
|
17 | bi2.04 | |
|
18 | 16 17 | bitri | |
19 | 18 | albii | |
20 | dfss2 | |
|
21 | 20 | imbi2i | |
22 | 15 19 21 | 3bitr4i | |
23 | 22 | albii | |
24 | 14 23 | bitri | |
25 | 5 24 | bitri | |
26 | dfss2 | |
|
27 | df-ral | |
|
28 | 25 26 27 | 3bitr4i | |