Step |
Hyp |
Ref |
Expression |
1 |
|
upgr1elem.s |
|- ( ph -> { B , C } e. S ) |
2 |
|
upgr1elem.b |
|- ( ph -> B e. W ) |
3 |
|
fveq2 |
|- ( x = { B , C } -> ( # ` x ) = ( # ` { B , C } ) ) |
4 |
3
|
breq1d |
|- ( x = { B , C } -> ( ( # ` x ) <_ 2 <-> ( # ` { B , C } ) <_ 2 ) ) |
5 |
|
prnzg |
|- ( B e. W -> { B , C } =/= (/) ) |
6 |
2 5
|
syl |
|- ( ph -> { B , C } =/= (/) ) |
7 |
|
eldifsn |
|- ( { B , C } e. ( S \ { (/) } ) <-> ( { B , C } e. S /\ { B , C } =/= (/) ) ) |
8 |
1 6 7
|
sylanbrc |
|- ( ph -> { B , C } e. ( S \ { (/) } ) ) |
9 |
|
hashprlei |
|- ( { B , C } e. Fin /\ ( # ` { B , C } ) <_ 2 ) |
10 |
9
|
simpri |
|- ( # ` { B , C } ) <_ 2 |
11 |
10
|
a1i |
|- ( ph -> ( # ` { B , C } ) <_ 2 ) |
12 |
4 8 11
|
elrabd |
|- ( ph -> { B , C } e. { x e. ( S \ { (/) } ) | ( # ` x ) <_ 2 } ) |
13 |
12
|
snssd |
|- ( ph -> { { B , C } } C_ { x e. ( S \ { (/) } ) | ( # ` x ) <_ 2 } ) |