Step |
Hyp |
Ref |
Expression |
1 |
|
elex |
|- ( A e. Singletons -> A e. _V ) |
2 |
|
snex |
|- { x } e. _V |
3 |
|
eleq1 |
|- ( A = { x } -> ( A e. _V <-> { x } e. _V ) ) |
4 |
2 3
|
mpbiri |
|- ( A = { x } -> A e. _V ) |
5 |
4
|
exlimiv |
|- ( E. x A = { x } -> A e. _V ) |
6 |
|
eleq1 |
|- ( y = A -> ( y e. Singletons <-> A e. Singletons ) ) |
7 |
|
eqeq1 |
|- ( y = A -> ( y = { x } <-> A = { x } ) ) |
8 |
7
|
exbidv |
|- ( y = A -> ( E. x y = { x } <-> E. x A = { x } ) ) |
9 |
|
df-singles |
|- Singletons = ran Singleton |
10 |
9
|
eleq2i |
|- ( y e. Singletons <-> y e. ran Singleton ) |
11 |
|
vex |
|- y e. _V |
12 |
11
|
elrn |
|- ( y e. ran Singleton <-> E. x x Singleton y ) |
13 |
|
vex |
|- x e. _V |
14 |
13 11
|
brsingle |
|- ( x Singleton y <-> y = { x } ) |
15 |
14
|
exbii |
|- ( E. x x Singleton y <-> E. x y = { x } ) |
16 |
10 12 15
|
3bitri |
|- ( y e. Singletons <-> E. x y = { x } ) |
17 |
6 8 16
|
vtoclbg |
|- ( A e. _V -> ( A e. Singletons <-> E. x A = { x } ) ) |
18 |
1 5 17
|
pm5.21nii |
|- ( A e. Singletons <-> E. x A = { x } ) |