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Theorem fodomfir 9340
Description: There exists a mapping from a finite set onto any nonempty set that it dominates, proved without using the Axiom of Power Sets (unlike fodomr 9142). (Contributed by BTernaryTau, 23-Jun-2025.)
Assertion
Ref Expression
fodomfir ((𝐴 ∈ Fin ∧ ∅ ≺ 𝐵𝐵𝐴) → ∃𝑓 𝑓:𝐴onto𝐵)
Distinct variable groups:   𝐴,𝑓   𝐵,𝑓

Proof of Theorem fodomfir
Dummy variables 𝑔 𝑧 are mutually distinct and distinct from all other variables.
StepHypRef Expression
1 relsdom 8966 . . . . . . 7 Rel ≺
21brrelex2i 5711 . . . . . 6 (∅ ≺ 𝐵𝐵 ∈ V)
3 0sdomg 9118 . . . . . . 7 (𝐵 ∈ V → (∅ ≺ 𝐵𝐵 ≠ ∅))
4 n0 4328 . . . . . . 7 (𝐵 ≠ ∅ ↔ ∃𝑧 𝑧𝐵)
53, 4bitrdi 287 . . . . . 6 (𝐵 ∈ V → (∅ ≺ 𝐵 ↔ ∃𝑧 𝑧𝐵))
62, 5syl 17 . . . . 5 (∅ ≺ 𝐵 → (∅ ≺ 𝐵 ↔ ∃𝑧 𝑧𝐵))
76ibi 267 . . . 4 (∅ ≺ 𝐵 → ∃𝑧 𝑧𝐵)
8 domfi 9203 . . . . . 6 ((𝐴 ∈ Fin ∧ 𝐵𝐴) → 𝐵 ∈ Fin)
9 simpl 482 . . . . . 6 ((𝐴 ∈ Fin ∧ 𝐵𝐴) → 𝐴 ∈ Fin)
10 brdomi 8973 . . . . . . . 8 (𝐵𝐴 → ∃𝑔 𝑔:𝐵1-1𝐴)
11 f1fn 6775 . . . . . . . . . . . 12 (𝑔:𝐵1-1𝐴𝑔 Fn 𝐵)
12 fnfi 9192 . . . . . . . . . . . 12 ((𝑔 Fn 𝐵𝐵 ∈ Fin) → 𝑔 ∈ Fin)
1311, 12sylan 580 . . . . . . . . . . 11 ((𝑔:𝐵1-1𝐴𝐵 ∈ Fin) → 𝑔 ∈ Fin)
1413ex 412 . . . . . . . . . 10 (𝑔:𝐵1-1𝐴 → (𝐵 ∈ Fin → 𝑔 ∈ Fin))
15 cnvfi 9190 . . . . . . . . . . . . . 14 (𝑔 ∈ Fin → 𝑔 ∈ Fin)
16 diffi 9189 . . . . . . . . . . . . . . 15 (𝐴 ∈ Fin → (𝐴 ∖ ran 𝑔) ∈ Fin)
17 snfi 9057 . . . . . . . . . . . . . . 15 {𝑧} ∈ Fin
18 xpfi 9330 . . . . . . . . . . . . . . 15 (((𝐴 ∖ ran 𝑔) ∈ Fin ∧ {𝑧} ∈ Fin) → ((𝐴 ∖ ran 𝑔) × {𝑧}) ∈ Fin)
1916, 17, 18sylancl 586 . . . . . . . . . . . . . 14 (𝐴 ∈ Fin → ((𝐴 ∖ ran 𝑔) × {𝑧}) ∈ Fin)
20 unfi 9185 . . . . . . . . . . . . . 14 ((𝑔 ∈ Fin ∧ ((𝐴 ∖ ran 𝑔) × {𝑧}) ∈ Fin) → (𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) ∈ Fin)
2115, 19, 20syl2an 596 . . . . . . . . . . . . 13 ((𝑔 ∈ Fin ∧ 𝐴 ∈ Fin) → (𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) ∈ Fin)
22 df-f1 6536 . . . . . . . . . . . . . . . . . . 19 (𝑔:𝐵1-1𝐴 ↔ (𝑔:𝐵𝐴 ∧ Fun 𝑔))
2322simprbi 496 . . . . . . . . . . . . . . . . . 18 (𝑔:𝐵1-1𝐴 → Fun 𝑔)
24 vex 3463 . . . . . . . . . . . . . . . . . . . 20 𝑧 ∈ V
2524fconst 6764 . . . . . . . . . . . . . . . . . . 19 ((𝐴 ∖ ran 𝑔) × {𝑧}):(𝐴 ∖ ran 𝑔)⟶{𝑧}
26 ffun 6709 . . . . . . . . . . . . . . . . . . 19 (((𝐴 ∖ ran 𝑔) × {𝑧}):(𝐴 ∖ ran 𝑔)⟶{𝑧} → Fun ((𝐴 ∖ ran 𝑔) × {𝑧}))
2725, 26ax-mp 5 . . . . . . . . . . . . . . . . . 18 Fun ((𝐴 ∖ ran 𝑔) × {𝑧})
2823, 27jctir 520 . . . . . . . . . . . . . . . . 17 (𝑔:𝐵1-1𝐴 → (Fun 𝑔 ∧ Fun ((𝐴 ∖ ran 𝑔) × {𝑧})))
29 df-rn 5665 . . . . . . . . . . . . . . . . . . . 20 ran 𝑔 = dom 𝑔
3029eqcomi 2744 . . . . . . . . . . . . . . . . . . 19 dom 𝑔 = ran 𝑔
3124snnz 4752 . . . . . . . . . . . . . . . . . . . 20 {𝑧} ≠ ∅
32 dmxp 5908 . . . . . . . . . . . . . . . . . . . 20 ({𝑧} ≠ ∅ → dom ((𝐴 ∖ ran 𝑔) × {𝑧}) = (𝐴 ∖ ran 𝑔))
3331, 32ax-mp 5 . . . . . . . . . . . . . . . . . . 19 dom ((𝐴 ∖ ran 𝑔) × {𝑧}) = (𝐴 ∖ ran 𝑔)
3430, 33ineq12i 4193 . . . . . . . . . . . . . . . . . 18 (dom 𝑔 ∩ dom ((𝐴 ∖ ran 𝑔) × {𝑧})) = (ran 𝑔 ∩ (𝐴 ∖ ran 𝑔))
35 disjdif 4447 . . . . . . . . . . . . . . . . . 18 (ran 𝑔 ∩ (𝐴 ∖ ran 𝑔)) = ∅
3634, 35eqtri 2758 . . . . . . . . . . . . . . . . 17 (dom 𝑔 ∩ dom ((𝐴 ∖ ran 𝑔) × {𝑧})) = ∅
37 funun 6582 . . . . . . . . . . . . . . . . 17 (((Fun 𝑔 ∧ Fun ((𝐴 ∖ ran 𝑔) × {𝑧})) ∧ (dom 𝑔 ∩ dom ((𝐴 ∖ ran 𝑔) × {𝑧})) = ∅) → Fun (𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})))
3828, 36, 37sylancl 586 . . . . . . . . . . . . . . . 16 (𝑔:𝐵1-1𝐴 → Fun (𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})))
3938adantl 481 . . . . . . . . . . . . . . 15 ((𝑧𝐵𝑔:𝐵1-1𝐴) → Fun (𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})))
40 dmun 5890 . . . . . . . . . . . . . . . . . 18 dom (𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) = (dom 𝑔 ∪ dom ((𝐴 ∖ ran 𝑔) × {𝑧}))
4129uneq1i 4139 . . . . . . . . . . . . . . . . . 18 (ran 𝑔 ∪ dom ((𝐴 ∖ ran 𝑔) × {𝑧})) = (dom 𝑔 ∪ dom ((𝐴 ∖ ran 𝑔) × {𝑧}))
4233uneq2i 4140 . . . . . . . . . . . . . . . . . 18 (ran 𝑔 ∪ dom ((𝐴 ∖ ran 𝑔) × {𝑧})) = (ran 𝑔 ∪ (𝐴 ∖ ran 𝑔))
4340, 41, 423eqtr2i 2764 . . . . . . . . . . . . . . . . 17 dom (𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) = (ran 𝑔 ∪ (𝐴 ∖ ran 𝑔))
44 f1f 6774 . . . . . . . . . . . . . . . . . . 19 (𝑔:𝐵1-1𝐴𝑔:𝐵𝐴)
4544frnd 6714 . . . . . . . . . . . . . . . . . 18 (𝑔:𝐵1-1𝐴 → ran 𝑔𝐴)
46 undif 4457 . . . . . . . . . . . . . . . . . 18 (ran 𝑔𝐴 ↔ (ran 𝑔 ∪ (𝐴 ∖ ran 𝑔)) = 𝐴)
4745, 46sylib 218 . . . . . . . . . . . . . . . . 17 (𝑔:𝐵1-1𝐴 → (ran 𝑔 ∪ (𝐴 ∖ ran 𝑔)) = 𝐴)
4843, 47eqtrid 2782 . . . . . . . . . . . . . . . 16 (𝑔:𝐵1-1𝐴 → dom (𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) = 𝐴)
4948adantl 481 . . . . . . . . . . . . . . 15 ((𝑧𝐵𝑔:𝐵1-1𝐴) → dom (𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) = 𝐴)
50 df-fn 6534 . . . . . . . . . . . . . . 15 ((𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) Fn 𝐴 ↔ (Fun (𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) ∧ dom (𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) = 𝐴))
5139, 49, 50sylanbrc 583 . . . . . . . . . . . . . 14 ((𝑧𝐵𝑔:𝐵1-1𝐴) → (𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) Fn 𝐴)
52 rnun 6134 . . . . . . . . . . . . . . 15 ran (𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) = (ran 𝑔 ∪ ran ((𝐴 ∖ ran 𝑔) × {𝑧}))
53 dfdm4 5875 . . . . . . . . . . . . . . . . . 18 dom 𝑔 = ran 𝑔
54 f1dm 6778 . . . . . . . . . . . . . . . . . 18 (𝑔:𝐵1-1𝐴 → dom 𝑔 = 𝐵)
5553, 54eqtr3id 2784 . . . . . . . . . . . . . . . . 17 (𝑔:𝐵1-1𝐴 → ran 𝑔 = 𝐵)
5655uneq1d 4142 . . . . . . . . . . . . . . . 16 (𝑔:𝐵1-1𝐴 → (ran 𝑔 ∪ ran ((𝐴 ∖ ran 𝑔) × {𝑧})) = (𝐵 ∪ ran ((𝐴 ∖ ran 𝑔) × {𝑧})))
57 xpeq1 5668 . . . . . . . . . . . . . . . . . . . . . . 23 ((𝐴 ∖ ran 𝑔) = ∅ → ((𝐴 ∖ ran 𝑔) × {𝑧}) = (∅ × {𝑧}))
58 0xp 5753 . . . . . . . . . . . . . . . . . . . . . . 23 (∅ × {𝑧}) = ∅
5957, 58eqtrdi 2786 . . . . . . . . . . . . . . . . . . . . . 22 ((𝐴 ∖ ran 𝑔) = ∅ → ((𝐴 ∖ ran 𝑔) × {𝑧}) = ∅)
6059rneqd 5918 . . . . . . . . . . . . . . . . . . . . 21 ((𝐴 ∖ ran 𝑔) = ∅ → ran ((𝐴 ∖ ran 𝑔) × {𝑧}) = ran ∅)
61 rn0 5905 . . . . . . . . . . . . . . . . . . . . 21 ran ∅ = ∅
6260, 61eqtrdi 2786 . . . . . . . . . . . . . . . . . . . 20 ((𝐴 ∖ ran 𝑔) = ∅ → ran ((𝐴 ∖ ran 𝑔) × {𝑧}) = ∅)
63 0ss 4375 . . . . . . . . . . . . . . . . . . . 20 ∅ ⊆ 𝐵
6462, 63eqsstrdi 4003 . . . . . . . . . . . . . . . . . . 19 ((𝐴 ∖ ran 𝑔) = ∅ → ran ((𝐴 ∖ ran 𝑔) × {𝑧}) ⊆ 𝐵)
6564a1d 25 . . . . . . . . . . . . . . . . . 18 ((𝐴 ∖ ran 𝑔) = ∅ → (𝑧𝐵 → ran ((𝐴 ∖ ran 𝑔) × {𝑧}) ⊆ 𝐵))
66 rnxp 6159 . . . . . . . . . . . . . . . . . . . . 21 ((𝐴 ∖ ran 𝑔) ≠ ∅ → ran ((𝐴 ∖ ran 𝑔) × {𝑧}) = {𝑧})
6766adantr 480 . . . . . . . . . . . . . . . . . . . 20 (((𝐴 ∖ ran 𝑔) ≠ ∅ ∧ 𝑧𝐵) → ran ((𝐴 ∖ ran 𝑔) × {𝑧}) = {𝑧})
68 snssi 4784 . . . . . . . . . . . . . . . . . . . . 21 (𝑧𝐵 → {𝑧} ⊆ 𝐵)
6968adantl 481 . . . . . . . . . . . . . . . . . . . 20 (((𝐴 ∖ ran 𝑔) ≠ ∅ ∧ 𝑧𝐵) → {𝑧} ⊆ 𝐵)
7067, 69eqsstrd 3993 . . . . . . . . . . . . . . . . . . 19 (((𝐴 ∖ ran 𝑔) ≠ ∅ ∧ 𝑧𝐵) → ran ((𝐴 ∖ ran 𝑔) × {𝑧}) ⊆ 𝐵)
7170ex 412 . . . . . . . . . . . . . . . . . 18 ((𝐴 ∖ ran 𝑔) ≠ ∅ → (𝑧𝐵 → ran ((𝐴 ∖ ran 𝑔) × {𝑧}) ⊆ 𝐵))
7265, 71pm2.61ine 3015 . . . . . . . . . . . . . . . . 17 (𝑧𝐵 → ran ((𝐴 ∖ ran 𝑔) × {𝑧}) ⊆ 𝐵)
73 ssequn2 4164 . . . . . . . . . . . . . . . . 17 (ran ((𝐴 ∖ ran 𝑔) × {𝑧}) ⊆ 𝐵 ↔ (𝐵 ∪ ran ((𝐴 ∖ ran 𝑔) × {𝑧})) = 𝐵)
7472, 73sylib 218 . . . . . . . . . . . . . . . 16 (𝑧𝐵 → (𝐵 ∪ ran ((𝐴 ∖ ran 𝑔) × {𝑧})) = 𝐵)
7556, 74sylan9eqr 2792 . . . . . . . . . . . . . . 15 ((𝑧𝐵𝑔:𝐵1-1𝐴) → (ran 𝑔 ∪ ran ((𝐴 ∖ ran 𝑔) × {𝑧})) = 𝐵)
7652, 75eqtrid 2782 . . . . . . . . . . . . . 14 ((𝑧𝐵𝑔:𝐵1-1𝐴) → ran (𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) = 𝐵)
77 df-fo 6537 . . . . . . . . . . . . . 14 ((𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})):𝐴onto𝐵 ↔ ((𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) Fn 𝐴 ∧ ran (𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) = 𝐵))
7851, 76, 77sylanbrc 583 . . . . . . . . . . . . 13 ((𝑧𝐵𝑔:𝐵1-1𝐴) → (𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})):𝐴onto𝐵)
79 foeq1 6786 . . . . . . . . . . . . . 14 (𝑓 = (𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) → (𝑓:𝐴onto𝐵 ↔ (𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})):𝐴onto𝐵))
8079spcegv 3576 . . . . . . . . . . . . 13 ((𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) ∈ Fin → ((𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})):𝐴onto𝐵 → ∃𝑓 𝑓:𝐴onto𝐵))
8121, 78, 80syl2im 40 . . . . . . . . . . . 12 ((𝑔 ∈ Fin ∧ 𝐴 ∈ Fin) → ((𝑧𝐵𝑔:𝐵1-1𝐴) → ∃𝑓 𝑓:𝐴onto𝐵))
8281expcomd 416 . . . . . . . . . . 11 ((𝑔 ∈ Fin ∧ 𝐴 ∈ Fin) → (𝑔:𝐵1-1𝐴 → (𝑧𝐵 → ∃𝑓 𝑓:𝐴onto𝐵)))
8382com12 32 . . . . . . . . . 10 (𝑔:𝐵1-1𝐴 → ((𝑔 ∈ Fin ∧ 𝐴 ∈ Fin) → (𝑧𝐵 → ∃𝑓 𝑓:𝐴onto𝐵)))
8414, 83syland 603 . . . . . . . . 9 (𝑔:𝐵1-1𝐴 → ((𝐵 ∈ Fin ∧ 𝐴 ∈ Fin) → (𝑧𝐵 → ∃𝑓 𝑓:𝐴onto𝐵)))
8584exlimiv 1930 . . . . . . . 8 (∃𝑔 𝑔:𝐵1-1𝐴 → ((𝐵 ∈ Fin ∧ 𝐴 ∈ Fin) → (𝑧𝐵 → ∃𝑓 𝑓:𝐴onto𝐵)))
8610, 85syl 17 . . . . . . 7 (𝐵𝐴 → ((𝐵 ∈ Fin ∧ 𝐴 ∈ Fin) → (𝑧𝐵 → ∃𝑓 𝑓:𝐴onto𝐵)))
8786adantl 481 . . . . . 6 ((𝐴 ∈ Fin ∧ 𝐵𝐴) → ((𝐵 ∈ Fin ∧ 𝐴 ∈ Fin) → (𝑧𝐵 → ∃𝑓 𝑓:𝐴onto𝐵)))
888, 9, 87mp2and 699 . . . . 5 ((𝐴 ∈ Fin ∧ 𝐵𝐴) → (𝑧𝐵 → ∃𝑓 𝑓:𝐴onto𝐵))
8988exlimdv 1933 . . . 4 ((𝐴 ∈ Fin ∧ 𝐵𝐴) → (∃𝑧 𝑧𝐵 → ∃𝑓 𝑓:𝐴onto𝐵))
907, 89syl5 34 . . 3 ((𝐴 ∈ Fin ∧ 𝐵𝐴) → (∅ ≺ 𝐵 → ∃𝑓 𝑓:𝐴onto𝐵))
91903impia 1117 . 2 ((𝐴 ∈ Fin ∧ 𝐵𝐴 ∧ ∅ ≺ 𝐵) → ∃𝑓 𝑓:𝐴onto𝐵)
92913com23 1126 1 ((𝐴 ∈ Fin ∧ ∅ ≺ 𝐵𝐵𝐴) → ∃𝑓 𝑓:𝐴onto𝐵)
Colors of variables: wff setvar class
Syntax hints:  wi 4  wb 206  wa 395  w3a 1086   = wceq 1540  wex 1779  wcel 2108  wne 2932  Vcvv 3459  cdif 3923  cun 3924  cin 3925  wss 3926  c0 4308  {csn 4601   class class class wbr 5119   × cxp 5652  ccnv 5653  dom cdm 5654  ran crn 5655  Fun wfun 6525   Fn wfn 6526  wf 6527  1-1wf1 6528  ontowfo 6529  cdom 8957  csdm 8958  Fincfn 8959
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1795  ax-4 1809  ax-5 1910  ax-6 1967  ax-7 2007  ax-8 2110  ax-9 2118  ax-10 2141  ax-11 2157  ax-12 2177  ax-ext 2707  ax-sep 5266  ax-nul 5276  ax-pr 5402  ax-un 7729
This theorem depends on definitions:  df-bi 207  df-an 396  df-or 848  df-3or 1087  df-3an 1088  df-tru 1543  df-fal 1553  df-ex 1780  df-nf 1784  df-sb 2065  df-mo 2539  df-eu 2568  df-clab 2714  df-cleq 2727  df-clel 2809  df-nfc 2885  df-ne 2933  df-ral 3052  df-rex 3061  df-reu 3360  df-rab 3416  df-v 3461  df-sbc 3766  df-dif 3929  df-un 3931  df-in 3933  df-ss 3943  df-pss 3946  df-nul 4309  df-if 4501  df-pw 4577  df-sn 4602  df-pr 4604  df-op 4608  df-uni 4884  df-br 5120  df-opab 5182  df-mpt 5202  df-tr 5230  df-id 5548  df-eprel 5553  df-po 5561  df-so 5562  df-fr 5606  df-we 5608  df-xp 5660  df-rel 5661  df-cnv 5662  df-co 5663  df-dm 5664  df-rn 5665  df-res 5666  df-ima 5667  df-ord 6355  df-on 6356  df-lim 6357  df-suc 6358  df-iota 6484  df-fun 6533  df-fn 6534  df-f 6535  df-f1 6536  df-fo 6537  df-f1o 6538  df-fv 6539  df-om 7862  df-1o 8480  df-en 8960  df-dom 8961  df-sdom 8962  df-fin 8963
This theorem is referenced by:  fodomfib  9341
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