Step |
Hyp |
Ref |
Expression |
1 |
|
fof |
|- ( f : A -onto-> B -> f : A --> B ) |
2 |
1
|
fdmd |
|- ( f : A -onto-> B -> dom f = A ) |
3 |
2
|
eqeq1d |
|- ( f : A -onto-> B -> ( dom f = (/) <-> A = (/) ) ) |
4 |
|
dm0rn0 |
|- ( dom f = (/) <-> ran f = (/) ) |
5 |
|
forn |
|- ( f : A -onto-> B -> ran f = B ) |
6 |
5
|
eqeq1d |
|- ( f : A -onto-> B -> ( ran f = (/) <-> B = (/) ) ) |
7 |
4 6
|
syl5bb |
|- ( f : A -onto-> B -> ( dom f = (/) <-> B = (/) ) ) |
8 |
3 7
|
bitr3d |
|- ( f : A -onto-> B -> ( A = (/) <-> B = (/) ) ) |
9 |
8
|
necon3bid |
|- ( f : A -onto-> B -> ( A =/= (/) <-> B =/= (/) ) ) |
10 |
9
|
biimpac |
|- ( ( A =/= (/) /\ f : A -onto-> B ) -> B =/= (/) ) |
11 |
10
|
adantll |
|- ( ( ( A e. Fin /\ A =/= (/) ) /\ f : A -onto-> B ) -> B =/= (/) ) |
12 |
|
vex |
|- f e. _V |
13 |
12
|
rnex |
|- ran f e. _V |
14 |
5 13
|
eqeltrrdi |
|- ( f : A -onto-> B -> B e. _V ) |
15 |
14
|
adantl |
|- ( ( A e. Fin /\ f : A -onto-> B ) -> B e. _V ) |
16 |
|
0sdomg |
|- ( B e. _V -> ( (/) ~< B <-> B =/= (/) ) ) |
17 |
15 16
|
syl |
|- ( ( A e. Fin /\ f : A -onto-> B ) -> ( (/) ~< B <-> B =/= (/) ) ) |
18 |
17
|
adantlr |
|- ( ( ( A e. Fin /\ A =/= (/) ) /\ f : A -onto-> B ) -> ( (/) ~< B <-> B =/= (/) ) ) |
19 |
11 18
|
mpbird |
|- ( ( ( A e. Fin /\ A =/= (/) ) /\ f : A -onto-> B ) -> (/) ~< B ) |
20 |
19
|
ex |
|- ( ( A e. Fin /\ A =/= (/) ) -> ( f : A -onto-> B -> (/) ~< B ) ) |
21 |
|
fodomfi |
|- ( ( A e. Fin /\ f : A -onto-> B ) -> B ~<_ A ) |
22 |
21
|
ex |
|- ( A e. Fin -> ( f : A -onto-> B -> B ~<_ A ) ) |
23 |
22
|
adantr |
|- ( ( A e. Fin /\ A =/= (/) ) -> ( f : A -onto-> B -> B ~<_ A ) ) |
24 |
20 23
|
jcad |
|- ( ( A e. Fin /\ A =/= (/) ) -> ( f : A -onto-> B -> ( (/) ~< B /\ B ~<_ A ) ) ) |
25 |
24
|
exlimdv |
|- ( ( A e. Fin /\ A =/= (/) ) -> ( E. f f : A -onto-> B -> ( (/) ~< B /\ B ~<_ A ) ) ) |
26 |
25
|
expimpd |
|- ( A e. Fin -> ( ( A =/= (/) /\ E. f f : A -onto-> B ) -> ( (/) ~< B /\ B ~<_ A ) ) ) |
27 |
|
sdomdomtr |
|- ( ( (/) ~< B /\ B ~<_ A ) -> (/) ~< A ) |
28 |
|
0sdomg |
|- ( A e. Fin -> ( (/) ~< A <-> A =/= (/) ) ) |
29 |
27 28
|
syl5ib |
|- ( A e. Fin -> ( ( (/) ~< B /\ B ~<_ A ) -> A =/= (/) ) ) |
30 |
|
fodomr |
|- ( ( (/) ~< B /\ B ~<_ A ) -> E. f f : A -onto-> B ) |
31 |
29 30
|
jca2 |
|- ( A e. Fin -> ( ( (/) ~< B /\ B ~<_ A ) -> ( A =/= (/) /\ E. f f : A -onto-> B ) ) ) |
32 |
26 31
|
impbid |
|- ( A e. Fin -> ( ( A =/= (/) /\ E. f f : A -onto-> B ) <-> ( (/) ~< B /\ B ~<_ A ) ) ) |