Description: The union of the successor of a set is equal to the binary union of that set with its union. (Contributed by NM, 30-Aug-1993) Extract from unisuc . (Revised by BJ, 28-Dec-2024)
Ref | Expression | ||
---|---|---|---|
Assertion | unisucs | |- ( A e. V -> U. suc A = ( U. A u. A ) ) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | df-suc | |- suc A = ( A u. { A } ) |
|
2 | 1 | unieqi | |- U. suc A = U. ( A u. { A } ) |
3 | 2 | a1i | |- ( A e. V -> U. suc A = U. ( A u. { A } ) ) |
4 | uniun | |- U. ( A u. { A } ) = ( U. A u. U. { A } ) |
|
5 | 4 | a1i | |- ( A e. V -> U. ( A u. { A } ) = ( U. A u. U. { A } ) ) |
6 | unisng | |- ( A e. V -> U. { A } = A ) |
|
7 | 6 | uneq2d | |- ( A e. V -> ( U. A u. U. { A } ) = ( U. A u. A ) ) |
8 | 3 5 7 | 3eqtrd | |- ( A e. V -> U. suc A = ( U. A u. A ) ) |