Step |
Hyp |
Ref |
Expression |
1 |
|
0ex |
|- (/) e. _V |
2 |
|
vex |
|- y e. _V |
3 |
1 2
|
opnzi |
|- <. (/) , y >. =/= (/) |
4 |
3
|
nesymi |
|- -. (/) = <. (/) , y >. |
5 |
|
peano1 |
|- (/) e. _om |
6 |
|
df-finxp |
|- ( U ^^ (/) ) = { y | ( (/) e. _om /\ (/) = ( rec ( ( n e. _om , x e. _V |-> if ( ( n = 1o /\ x e. U ) , (/) , if ( x e. ( _V X. U ) , <. U. n , ( 1st ` x ) >. , <. n , x >. ) ) ) , <. (/) , y >. ) ` (/) ) ) } |
7 |
6
|
abeq2i |
|- ( y e. ( U ^^ (/) ) <-> ( (/) e. _om /\ (/) = ( rec ( ( n e. _om , x e. _V |-> if ( ( n = 1o /\ x e. U ) , (/) , if ( x e. ( _V X. U ) , <. U. n , ( 1st ` x ) >. , <. n , x >. ) ) ) , <. (/) , y >. ) ` (/) ) ) ) |
8 |
5 7
|
mpbiran |
|- ( y e. ( U ^^ (/) ) <-> (/) = ( rec ( ( n e. _om , x e. _V |-> if ( ( n = 1o /\ x e. U ) , (/) , if ( x e. ( _V X. U ) , <. U. n , ( 1st ` x ) >. , <. n , x >. ) ) ) , <. (/) , y >. ) ` (/) ) ) |
9 |
|
opex |
|- <. (/) , y >. e. _V |
10 |
9
|
rdg0 |
|- ( rec ( ( n e. _om , x e. _V |-> if ( ( n = 1o /\ x e. U ) , (/) , if ( x e. ( _V X. U ) , <. U. n , ( 1st ` x ) >. , <. n , x >. ) ) ) , <. (/) , y >. ) ` (/) ) = <. (/) , y >. |
11 |
10
|
eqeq2i |
|- ( (/) = ( rec ( ( n e. _om , x e. _V |-> if ( ( n = 1o /\ x e. U ) , (/) , if ( x e. ( _V X. U ) , <. U. n , ( 1st ` x ) >. , <. n , x >. ) ) ) , <. (/) , y >. ) ` (/) ) <-> (/) = <. (/) , y >. ) |
12 |
8 11
|
bitri |
|- ( y e. ( U ^^ (/) ) <-> (/) = <. (/) , y >. ) |
13 |
4 12
|
mtbir |
|- -. y e. ( U ^^ (/) ) |
14 |
13
|
nel0 |
|- ( U ^^ (/) ) = (/) |