Description: The second projection preserves unions. (Contributed by BJ, 6-Apr-2019)
Ref | Expression | ||
---|---|---|---|
Assertion | bj-pr2un | |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | bj-projun | |
|
2 | df-bj-pr2 | |
|
3 | df-bj-pr2 | |
|
4 | df-bj-pr2 | |
|
5 | 3 4 | uneq12i | |
6 | 1 2 5 | 3eqtr4i | |