Description: Define double indexed union. (Contributed by FL, 6-Nov-2013)
Ref | Expression | ||
---|---|---|---|
Assertion | dfiunv2 | |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | df-iun | |
|
2 | 1 | a1i | |
3 | 2 | iuneq2i | |
4 | df-iun | |
|
5 | vex | |
|
6 | eleq1w | |
|
7 | 6 | rexbidv | |
8 | 5 7 | elab | |
9 | 8 | rexbii | |
10 | 9 | abbii | |
11 | 3 4 10 | 3eqtri | |