Metamath Proof Explorer


Theorem unisucs

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 ) )

Proof

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 ) )