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Theorem dffo2 5221
Description: Alternate definition of an onto function. (Contributed by NM, 22-Mar-2006.)
Assertion
Ref Expression
dffo2 (𝐹:𝐴onto𝐵 ↔ (𝐹:𝐴𝐵 ∧ ran 𝐹 = 𝐵))

Proof of Theorem dffo2
StepHypRef Expression
1 fof 5217 . . 3 (𝐹:𝐴onto𝐵𝐹:𝐴𝐵)
2 forn 5220 . . 3 (𝐹:𝐴onto𝐵 → ran 𝐹 = 𝐵)
31, 2jca 300 . 2 (𝐹:𝐴onto𝐵 → (𝐹:𝐴𝐵 ∧ ran 𝐹 = 𝐵))
4 ffn 5147 . . 3 (𝐹:𝐴𝐵𝐹 Fn 𝐴)
5 df-fo 5008 . . . 4 (𝐹:𝐴onto𝐵 ↔ (𝐹 Fn 𝐴 ∧ ran 𝐹 = 𝐵))
65biimpri 131 . . 3 ((𝐹 Fn 𝐴 ∧ ran 𝐹 = 𝐵) → 𝐹:𝐴onto𝐵)
74, 6sylan 277 . 2 ((𝐹:𝐴𝐵 ∧ ran 𝐹 = 𝐵) → 𝐹:𝐴onto𝐵)
83, 7impbii 124 1 (𝐹:𝐴onto𝐵 ↔ (𝐹:𝐴𝐵 ∧ ran 𝐹 = 𝐵))
Colors of variables: wff set class
Syntax hints:  wa 102  wb 103   = wceq 1289  ran crn 4429   Fn wfn 4997  wf 4998  ontowfo 5000
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 104  ax-ia2 105  ax-ia3 106  ax-5 1381  ax-7 1382  ax-gen 1383  ax-ie1 1427  ax-ie2 1428  ax-8 1440  ax-11 1442  ax-4 1445  ax-17 1464  ax-i9 1468  ax-ial 1472  ax-i5r 1473  ax-ext 2070
This theorem depends on definitions:  df-bi 115  df-nf 1395  df-sb 1693  df-clab 2075  df-cleq 2081  df-clel 2084  df-in 3003  df-ss 3010  df-f 5006  df-fo 5008
This theorem is referenced by:  foco  5227  dff1o5  5246  dffo3  5430  dffo4  5431  fo1stresm  5914  fo2ndresm  5915  fo2ndf  5974  1fv  9515
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