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Metamath Proof Explorer

Theorem f1finf1o

Description: Any injection from one finite set to another of equal size must be a bijection. (Contributed by Jeff Madsen, 5-Jun-2010) (Revised by Mario Carneiro, 27-Feb-2014) Avoid ax-pow . (Revised by BTernaryTau, 4-Jan-2025)

Ref Expression
Assertion f1finf1o 
|- ( ( A ~~ B /\ B e. Fin ) -> ( F : A -1-1-> B <-> F : A -1-1-onto-> B ) )

Proof

Step Hyp Ref Expression
1 simpr 
 |-  ( ( ( A ~~ B /\ B e. Fin ) /\ F : A -1-1-> B ) -> F : A -1-1-> B )
2 f1f 
 |-  ( F : A -1-1-> B -> F : A --> B )
3 2 adantl 
 |-  ( ( ( A ~~ B /\ B e. Fin ) /\ F : A -1-1-> B ) -> F : A --> B )
4 3 ffnd 
 |-  ( ( ( A ~~ B /\ B e. Fin ) /\ F : A -1-1-> B ) -> F Fn A )
5 simpll 
 |-  ( ( ( A ~~ B /\ B e. Fin ) /\ F : A -1-1-> B ) -> A ~~ B )
6 3 frnd 
 |-  ( ( ( A ~~ B /\ B e. Fin ) /\ F : A -1-1-> B ) -> ran F C_ B )
7 df-pss 
 |-  ( ran F C. B <-> ( ran F C_ B /\ ran F =/= B ) )
8 7 baib 
 |-  ( ran F C_ B -> ( ran F C. B <-> ran F =/= B ) )
9 6 8 syl 
 |-  ( ( ( A ~~ B /\ B e. Fin ) /\ F : A -1-1-> B ) -> ( ran F C. B <-> ran F =/= B ) )
10 php3 
 |-  ( ( B e. Fin /\ ran F C. B ) -> ran F ~< B )
11 10 ex 
 |-  ( B e. Fin -> ( ran F C. B -> ran F ~< B ) )
12 11 ad2antlr 
 |-  ( ( ( A ~~ B /\ B e. Fin ) /\ F : A -1-1-> B ) -> ( ran F C. B -> ran F ~< B ) )
13 enfii 
 |-  ( ( B e. Fin /\ A ~~ B ) -> A e. Fin )
14 13 ancoms 
 |-  ( ( A ~~ B /\ B e. Fin ) -> A e. Fin )
15 f1f1orn 
 |-  ( F : A -1-1-> B -> F : A -1-1-onto-> ran F )
16 f1oenfi 
 |-  ( ( A e. Fin /\ F : A -1-1-onto-> ran F ) -> A ~~ ran F )
17 14 15 16 syl2an 
 |-  ( ( ( A ~~ B /\ B e. Fin ) /\ F : A -1-1-> B ) -> A ~~ ran F )
18 endom 
 |-  ( A ~~ ran F -> A ~<_ ran F )
19 domsdomtrfi 
 |-  ( ( A e. Fin /\ A ~<_ ran F /\ ran F ~< B ) -> A ~< B )
20 18 19 syl3an2 
 |-  ( ( A e. Fin /\ A ~~ ran F /\ ran F ~< B ) -> A ~< B )
21 20 3expia 
 |-  ( ( A e. Fin /\ A ~~ ran F ) -> ( ran F ~< B -> A ~< B ) )
22 14 17 21 syl2an2r 
 |-  ( ( ( A ~~ B /\ B e. Fin ) /\ F : A -1-1-> B ) -> ( ran F ~< B -> A ~< B ) )
23 12 22 syld 
 |-  ( ( ( A ~~ B /\ B e. Fin ) /\ F : A -1-1-> B ) -> ( ran F C. B -> A ~< B ) )
24 sdomnen 
 |-  ( A ~< B -> -. A ~~ B )
25 23 24 syl6 
 |-  ( ( ( A ~~ B /\ B e. Fin ) /\ F : A -1-1-> B ) -> ( ran F C. B -> -. A ~~ B ) )
26 9 25 sylbird 
 |-  ( ( ( A ~~ B /\ B e. Fin ) /\ F : A -1-1-> B ) -> ( ran F =/= B -> -. A ~~ B ) )
27 26 necon4ad 
 |-  ( ( ( A ~~ B /\ B e. Fin ) /\ F : A -1-1-> B ) -> ( A ~~ B -> ran F = B ) )
28 5 27 mpd 
 |-  ( ( ( A ~~ B /\ B e. Fin ) /\ F : A -1-1-> B ) -> ran F = B )
29 df-fo 
 |-  ( F : A -onto-> B <-> ( F Fn A /\ ran F = B ) )
30 4 28 29 sylanbrc 
 |-  ( ( ( A ~~ B /\ B e. Fin ) /\ F : A -1-1-> B ) -> F : A -onto-> B )
31 df-f1o 
 |-  ( F : A -1-1-onto-> B <-> ( F : A -1-1-> B /\ F : A -onto-> B ) )
32 1 30 31 sylanbrc 
 |-  ( ( ( A ~~ B /\ B e. Fin ) /\ F : A -1-1-> B ) -> F : A -1-1-onto-> B )
33 32 ex 
 |-  ( ( A ~~ B /\ B e. Fin ) -> ( F : A -1-1-> B -> F : A -1-1-onto-> B ) )
34 f1of1 
 |-  ( F : A -1-1-onto-> B -> F : A -1-1-> B )
35 33 34 impbid1 
 |-  ( ( A ~~ B /\ B e. Fin ) -> ( F : A -1-1-> B <-> F : A -1-1-onto-> B ) )