Metamath Proof Explorer


Theorem unidif0

Description: The removal of the empty set from a class does not affect its union. (Contributed by NM, 22-Mar-2004)

Ref Expression
Assertion unidif0 ( 𝐴 ∖ { ∅ } ) = 𝐴

Proof

Step Hyp Ref Expression
1 uniun ( ( 𝐴 ∖ { ∅ } ) ∪ { ∅ } ) = ( ( 𝐴 ∖ { ∅ } ) ∪ { ∅ } )
2 undif1 ( ( 𝐴 ∖ { ∅ } ) ∪ { ∅ } ) = ( 𝐴 ∪ { ∅ } )
3 uncom ( 𝐴 ∪ { ∅ } ) = ( { ∅ } ∪ 𝐴 )
4 2 3 eqtr2i ( { ∅ } ∪ 𝐴 ) = ( ( 𝐴 ∖ { ∅ } ) ∪ { ∅ } )
5 4 unieqi ( { ∅ } ∪ 𝐴 ) = ( ( 𝐴 ∖ { ∅ } ) ∪ { ∅ } )
6 0ex ∅ ∈ V
7 6 unisn { ∅ } = ∅
8 7 uneq2i ( ( 𝐴 ∖ { ∅ } ) ∪ { ∅ } ) = ( ( 𝐴 ∖ { ∅ } ) ∪ ∅ )
9 un0 ( ( 𝐴 ∖ { ∅ } ) ∪ ∅ ) = ( 𝐴 ∖ { ∅ } )
10 8 9 eqtr2i ( 𝐴 ∖ { ∅ } ) = ( ( 𝐴 ∖ { ∅ } ) ∪ { ∅ } )
11 1 5 10 3eqtr4ri ( 𝐴 ∖ { ∅ } ) = ( { ∅ } ∪ 𝐴 )
12 uniun ( { ∅ } ∪ 𝐴 ) = ( { ∅ } ∪ 𝐴 )
13 7 uneq1i ( { ∅ } ∪ 𝐴 ) = ( ∅ ∪ 𝐴 )
14 11 12 13 3eqtri ( 𝐴 ∖ { ∅ } ) = ( ∅ ∪ 𝐴 )
15 uncom ( ∅ ∪ 𝐴 ) = ( 𝐴 ∪ ∅ )
16 un0 ( 𝐴 ∪ ∅ ) = 𝐴
17 14 15 16 3eqtri ( 𝐴 ∖ { ∅ } ) = 𝐴