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Theorem fodomfir 9357
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 9185). (Contributed by BTernaryTau, 23-Jun-2025.)
Assertion
Ref Expression
fodomfir ((𝐴 ∈ Fin ∧ ∅ ≺ 𝐵 ∧ 𝐵 ≼ 𝐴) → ∃𝑓 𝑓:𝐴⟶onto𝐵)
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 9018 . . . . . . 7 Rel ≺
21brrelex2i 5715 . . . . . 6 (∅ ≺ 𝐵 → 𝐵 ∈ V)
3 0sdomg 9163 . . . . . . 7 (𝐵 ∈ V → (∅ ≺ 𝐵 ↔ 𝐵 ≠ ∅))
4 n0 4303 . . . . . . 7 (𝐵 ≠ ∅ ↔ ∃𝑧 𝑧 ∈ 𝐵)
53, 4bitrdi 290 . . . . . 6 (𝐵 ∈ V → (∅ ≺ 𝐵 ↔ ∃𝑧 𝑧 ∈ 𝐵))
62, 5syl 18 . . . . 5 (∅ ≺ 𝐵 → (∅ ≺ 𝐵 ↔ ∃𝑧 𝑧 ∈ 𝐵))
76ibi 270 . . . 4 (∅ ≺ 𝐵 → ∃𝑧 𝑧 ∈ 𝐵)
8 domfi 9242 . . . . . 6 ((𝐴 ∈ Fin ∧ 𝐵 ≼ 𝐴) → 𝐵 ∈ Fin)
9 simpl 488 . . . . . 6 ((𝐴 ∈ Fin ∧ 𝐵 ≼ 𝐴) → 𝐴 ∈ Fin)
10 brdomi 9024 . . . . . . . 8 (𝐵 ≼ 𝐴 → ∃𝑔 𝑔:𝐵⟶1-1𝐴)
11 f1fn 6809 . . . . . . . . . . . 12 (𝑔:𝐵⟶1-1𝐴 → 𝑔 Fn 𝐵)
12 fnfi 9231 . . . . . . . . . . . 12 ((𝑔 Fn 𝐵 ∧ 𝐵 ∈ Fin) → 𝑔 ∈ Fin)
1311, 12sylan 592 . . . . . . . . . . 11 ((𝑔:𝐵⟶1-1𝐴 ∧ 𝐵 ∈ Fin) → 𝑔 ∈ Fin)
1413ex 418 . . . . . . . . . 10 (𝑔:𝐵⟶1-1𝐴 → (𝐵 ∈ Fin → 𝑔 ∈ Fin))
15 cnvfi 9229 . . . . . . . . . . . . . 14 (𝑔 ∈ Fin → ◡𝑔 ∈ Fin)
16 diffi 9228 . . . . . . . . . . . . . . 15 (𝐴 ∈ Fin → (𝐴 ∖ ran 𝑔) ∈ Fin)
17 snfi 9109 . . . . . . . . . . . . . . 15 {𝑧} ∈ Fin
18 xpfi 9349 . . . . . . . . . . . . . . 15 (((𝐴 ∖ ran 𝑔) ∈ Fin ∧ {𝑧} ∈ Fin) → ((𝐴 ∖ ran 𝑔) × {𝑧}) ∈ Fin)
1916, 17, 18sylancl 598 . . . . . . . . . . . . . 14 (𝐴 ∈ Fin → ((𝐴 ∖ ran 𝑔) × {𝑧}) ∈ Fin)
20 unfi 9224 . . . . . . . . . . . . . 14 ((◡𝑔 ∈ Fin ∧ ((𝐴 ∖ ran 𝑔) × {𝑧}) ∈ Fin) → (◡𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) ∈ Fin)
2115, 19, 20syl2an 608 . . . . . . . . . . . . 13 ((𝑔 ∈ Fin ∧ 𝐴 ∈ Fin) → (◡𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) ∈ Fin)
22 df-f1 6571 . . . . . . . . . . . . . . . . . . 19 (𝑔:𝐵⟶1-1𝐴 ↔ (𝑔:𝐵⟶𝐴 ∧ Fun ◡𝑔))
2322simprbi 503 . . . . . . . . . . . . . . . . . 18 (𝑔:𝐵⟶1-1𝐴 → Fun ◡𝑔)
24 vex 3458 . . . . . . . . . . . . . . . . . . . 20 𝑧 ∈ V
2524fconst 6798 . . . . . . . . . . . . . . . . . . 19 ((𝐴 ∖ ran 𝑔) × {𝑧}):(𝐴 ∖ ran 𝑔)⟶{𝑧}
26 ffun 6742 . . . . . . . . . . . . . . . . . . 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 530 . . . . . . . . . . . . . . . . 17 (𝑔:𝐵⟶1-1𝐴 → (Fun ◡𝑔 ∧ Fun ((𝐴 ∖ ran 𝑔) × {𝑧})))
29 df-rn 5669 . . . . . . . . . . . . . . . . . . . 20 ran 𝑔 = dom ◡𝑔
3029eqcomi 2772 . . . . . . . . . . . . . . . . . . 19 dom ◡𝑔 = ran 𝑔
3124snnz 4739 . . . . . . . . . . . . . . . . . . . 20 {𝑧} ≠ ∅
32 dmxp 5923 . . . . . . . . . . . . . . . . . . . 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 4118 . . . . . . . . . . . . . . . . . 18 (dom ◡𝑔 ∩ dom ((𝐴 ∖ ran 𝑔) × {𝑧})) = (ran 𝑔 ∩ (𝐴 ∖ ran 𝑔))
35 disjdif 4429 . . . . . . . . . . . . . . . . . 18 (ran 𝑔 ∩ (𝐴 ∖ ran 𝑔)) = ∅
3634, 35eqtri 2786 . . . . . . . . . . . . . . . . 17 (dom ◡𝑔 ∩ dom ((𝐴 ∖ ran 𝑔) × {𝑧})) = ∅
37 funun 6614 . . . . . . . . . . . . . . . . 17 (((Fun ◡𝑔 ∧ Fun ((𝐴 ∖ ran 𝑔) × {𝑧})) ∧ (dom ◡𝑔 ∩ dom ((𝐴 ∖ ran 𝑔) × {𝑧})) = ∅) → Fun (◡𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})))
3828, 36, 37sylancl 598 . . . . . . . . . . . . . . . 16 (𝑔:𝐵⟶1-1𝐴 → Fun (◡𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})))
3938adantl 487 . . . . . . . . . . . . . . 15 ((𝑧 ∈ 𝐵 ∧ 𝑔:𝐵⟶1-1𝐴) → Fun (◡𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})))
40 dmun 5904 . . . . . . . . . . . . . . . . . 18 dom (◡𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) = (dom ◡𝑔 ∪ dom ((𝐴 ∖ ran 𝑔) × {𝑧}))
4129uneq1i 4166 . . . . . . . . . . . . . . . . . 18 (ran 𝑔 ∪ dom ((𝐴 ∖ ran 𝑔) × {𝑧})) = (dom ◡𝑔 ∪ dom ((𝐴 ∖ ran 𝑔) × {𝑧}))
4233uneq2i 4167 . . . . . . . . . . . . . . . . . 18 (ran 𝑔 ∪ dom ((𝐴 ∖ ran 𝑔) × {𝑧})) = (ran 𝑔 ∪ (𝐴 ∖ ran 𝑔))
4340, 41, 423eqtr2i 2792 . . . . . . . . . . . . . . . . 17 dom (◡𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) = (ran 𝑔 ∪ (𝐴 ∖ ran 𝑔))
44 f1f 6808 . . . . . . . . . . . . . . . . . . 19 (𝑔:𝐵⟶1-1𝐴 → 𝑔:𝐵⟶𝐴)
4544frnd 6748 . . . . . . . . . . . . . . . . . 18 (𝑔:𝐵⟶1-1𝐴 → ran 𝑔 ⊆ 𝐴)
46 undif 4441 . . . . . . . . . . . . . . . . . 18 (ran 𝑔 ⊆ 𝐴 ↔ (ran 𝑔 ∪ (𝐴 ∖ ran 𝑔)) = 𝐴)
4745, 46sylib 221 . . . . . . . . . . . . . . . . 17 (𝑔:𝐵⟶1-1𝐴 → (ran 𝑔 ∪ (𝐴 ∖ ran 𝑔)) = 𝐴)
4843, 47eqtrid 2810 . . . . . . . . . . . . . . . 16 (𝑔:𝐵⟶1-1𝐴 → dom (◡𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) = 𝐴)
4948adantl 487 . . . . . . . . . . . . . . 15 ((𝑧 ∈ 𝐵 ∧ 𝑔:𝐵⟶1-1𝐴) → dom (◡𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) = 𝐴)
50 df-fn 6569 . . . . . . . . . . . . . . 15 ((◡𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) Fn 𝐴 ↔ (Fun (◡𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) ∧ dom (◡𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) = 𝐴))
5139, 49, 50sylanbrc 595 . . . . . . . . . . . . . 14 ((𝑧 ∈ 𝐵 ∧ 𝑔:𝐵⟶1-1𝐴) → (◡𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) Fn 𝐴)
52 rnun 6154 . . . . . . . . . . . . . . 15 ran (◡𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) = (ran ◡𝑔 ∪ ran ((𝐴 ∖ ran 𝑔) × {𝑧}))
53 dfdm4 5889 . . . . . . . . . . . . . . . . . 18 dom 𝑔 = ran ◡𝑔
54 f1dm 6814 . . . . . . . . . . . . . . . . . 18 (𝑔:𝐵⟶1-1𝐴 → dom 𝑔 = 𝐵)
5553, 54eqtr3id 2812 . . . . . . . . . . . . . . . . 17 (𝑔:𝐵⟶1-1𝐴 → ran ◡𝑔 = 𝐵)
5655uneq1d 4169 . . . . . . . . . . . . . . . 16 (𝑔:𝐵⟶1-1𝐴 → (ran ◡𝑔 ∪ ran ((𝐴 ∖ ran 𝑔) × {𝑧})) = (𝐵 ∪ ran ((𝐴 ∖ ran 𝑔) × {𝑧})))
57 xpeq1 5672 . . . . . . . . . . . . . . . . . . . . . . 23 ((𝐴 ∖ ran 𝑔) = ∅ → ((𝐴 ∖ ran 𝑔) × {𝑧}) = (∅ × {𝑧}))
58 0xp 5758 . . . . . . . . . . . . . . . . . . . . . . 23 (∅ × {𝑧}) = ∅
5957, 58eqtrdi 2814 . . . . . . . . . . . . . . . . . . . . . 22 ((𝐴 ∖ ran 𝑔) = ∅ → ((𝐴 ∖ ran 𝑔) × {𝑧}) = ∅)
6059rneqd 5932 . . . . . . . . . . . . . . . . . . . . 21 ((𝐴 ∖ ran 𝑔) = ∅ → ran ((𝐴 ∖ ran 𝑔) × {𝑧}) = ran ∅)
61 rn0 5920 . . . . . . . . . . . . . . . . . . . . 21 ran ∅ = ∅
6260, 61eqtrdi 2814 . . . . . . . . . . . . . . . . . . . 20 ((𝐴 ∖ ran 𝑔) = ∅ → ran ((𝐴 ∖ ran 𝑔) × {𝑧}) = ∅)
63 0ss 4353 . . . . . . . . . . . . . . . . . . . 20 ∅ ⊆ 𝐵
6462, 63eqsstrdi 3957 . . . . . . . . . . . . . . . . . . 19 ((𝐴 ∖ ran 𝑔) = ∅ → ran ((𝐴 ∖ ran 𝑔) × {𝑧}) ⊆ 𝐵)
6564a1d 26 . . . . . . . . . . . . . . . . . 18 ((𝐴 ∖ ran 𝑔) = ∅ → (𝑧 ∈ 𝐵 → ran ((𝐴 ∖ ran 𝑔) × {𝑧}) ⊆ 𝐵))
66 rnxp 6180 . . . . . . . . . . . . . . . . . . . . 21 ((𝐴 ∖ ran 𝑔) ≠ ∅ → ran ((𝐴 ∖ ran 𝑔) × {𝑧}) = {𝑧})
6766adantr 486 . . . . . . . . . . . . . . . . . . . 20 (((𝐴 ∖ ran 𝑔) ≠ ∅ ∧ 𝑧 ∈ 𝐵) → ran ((𝐴 ∖ ran 𝑔) × {𝑧}) = {𝑧})
68 snssi 4748 . . . . . . . . . . . . . . . . . . . . 21 (𝑧 ∈ 𝐵 → {𝑧} ⊆ 𝐵)
6968adantl 487 . . . . . . . . . . . . . . . . . . . 20 (((𝐴 ∖ ran 𝑔) ≠ ∅ ∧ 𝑧 ∈ 𝐵) → {𝑧} ⊆ 𝐵)
7067, 69eqsstrd 3947 . . . . . . . . . . . . . . . . . . 19 (((𝐴 ∖ ran 𝑔) ≠ ∅ ∧ 𝑧 ∈ 𝐵) → ran ((𝐴 ∖ ran 𝑔) × {𝑧}) ⊆ 𝐵)
7170ex 418 . . . . . . . . . . . . . . . . . 18 ((𝐴 ∖ ran 𝑔) ≠ ∅ → (𝑧 ∈ 𝐵 → ran ((𝐴 ∖ ran 𝑔) × {𝑧}) ⊆ 𝐵))
7265, 71pm2.61ine 3042 . . . . . . . . . . . . . . . . 17 (𝑧 ∈ 𝐵 → ran ((𝐴 ∖ ran 𝑔) × {𝑧}) ⊆ 𝐵)
73 ssequn2 4190 . . . . . . . . . . . . . . . . 17 (ran ((𝐴 ∖ ran 𝑔) × {𝑧}) ⊆ 𝐵 ↔ (𝐵 ∪ ran ((𝐴 ∖ ran 𝑔) × {𝑧})) = 𝐵)
7472, 73sylib 221 . . . . . . . . . . . . . . . 16 (𝑧 ∈ 𝐵 → (𝐵 ∪ ran ((𝐴 ∖ ran 𝑔) × {𝑧})) = 𝐵)
7556, 74sylan9eqr 2820 . . . . . . . . . . . . . . 15 ((𝑧 ∈ 𝐵 ∧ 𝑔:𝐵⟶1-1𝐴) → (ran ◡𝑔 ∪ ran ((𝐴 ∖ ran 𝑔) × {𝑧})) = 𝐵)
7652, 75eqtrid 2810 . . . . . . . . . . . . . 14 ((𝑧 ∈ 𝐵 ∧ 𝑔:𝐵⟶1-1𝐴) → ran (◡𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) = 𝐵)
77 df-fo 6572 . . . . . . . . . . . . . 14 ((◡𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})):𝐴⟶onto𝐵 ↔ ((◡𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) Fn 𝐴 ∧ ran (◡𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) = 𝐵))
7851, 76, 77sylanbrc 595 . . . . . . . . . . . . 13 ((𝑧 ∈ 𝐵 ∧ 𝑔:𝐵⟶1-1𝐴) → (◡𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})):𝐴⟶onto𝐵)
79 foeq1 6822 . . . . . . . . . . . . . 14 (𝑓 = (◡𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) → (𝑓:𝐴⟶onto𝐵 ↔ (◡𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})):𝐴⟶onto𝐵))
8079spcegv 3555 . . . . . . . . . . . . 13 ((◡𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) ∈ Fin → ((◡𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})):𝐴⟶onto𝐵 → ∃𝑓 𝑓:𝐴⟶onto𝐵))
8121, 78, 80syl2im 41 . . . . . . . . . . . 12 ((𝑔 ∈ Fin ∧ 𝐴 ∈ Fin) → ((𝑧 ∈ 𝐵 ∧ 𝑔:𝐵⟶1-1𝐴) → ∃𝑓 𝑓:𝐴⟶onto𝐵))
8281expcomd 422 . . . . . . . . . . 11 ((𝑔 ∈ Fin ∧ 𝐴 ∈ Fin) → (𝑔:𝐵⟶1-1𝐴 → (𝑧 ∈ 𝐵 → ∃𝑓 𝑓:𝐴⟶onto𝐵)))
8382com12 33 . . . . . . . . . 10 (𝑔:𝐵⟶1-1𝐴 → ((𝑔 ∈ Fin ∧ 𝐴 ∈ Fin) → (𝑧 ∈ 𝐵 → ∃𝑓 𝑓:𝐴⟶onto𝐵)))
8414, 83syland 615 . . . . . . . . 9 (𝑔:𝐵⟶1-1𝐴 → ((𝐵 ∈ Fin ∧ 𝐴 ∈ Fin) → (𝑧 ∈ 𝐵 → ∃𝑓 𝑓:𝐴⟶onto𝐵)))
8584exlimiv 1965 . . . . . . . 8 (∃𝑔 𝑔:𝐵⟶1-1𝐴 → ((𝐵 ∈ Fin ∧ 𝐴 ∈ Fin) → (𝑧 ∈ 𝐵 → ∃𝑓 𝑓:𝐴⟶onto𝐵)))
8610, 85syl 18 . . . . . . 7 (𝐵 ≼ 𝐴 → ((𝐵 ∈ Fin ∧ 𝐴 ∈ Fin) → (𝑧 ∈ 𝐵 → ∃𝑓 𝑓:𝐴⟶onto𝐵)))
8786adantl 487 . . . . . 6 ((𝐴 ∈ Fin ∧ 𝐵 ≼ 𝐴) → ((𝐵 ∈ Fin ∧ 𝐴 ∈ Fin) → (𝑧 ∈ 𝐵 → ∃𝑓 𝑓:𝐴⟶onto𝐵)))
888, 9, 87mp2and 712 . . . . 5 ((𝐴 ∈ Fin ∧ 𝐵 ≼ 𝐴) → (𝑧 ∈ 𝐵 → ∃𝑓 𝑓:𝐴⟶onto𝐵))
8988exlimdv 1968 . . . 4 ((𝐴 ∈ Fin ∧ 𝐵 ≼ 𝐴) → (∃𝑧 𝑧 ∈ 𝐵 → ∃𝑓 𝑓:𝐴⟶onto𝐵))
907, 89syl5 35 . . 3 ((𝐴 ∈ Fin ∧ 𝐵 ≼ 𝐴) → (∅ ≺ 𝐵 → ∃𝑓 𝑓:𝐴⟶onto𝐵))
91903impia 1135 . 2 ((𝐴 ∈ Fin ∧ 𝐵 ≼ 𝐴 ∧ ∅ ≺ 𝐵) → ∃𝑓 𝑓:𝐴⟶onto𝐵)
92913com23 1144 1 ((𝐴 ∈ Fin ∧ ∅ ≺ 𝐵 ∧ 𝐵 ≼ 𝐴) → ∃𝑓 𝑓:𝐴⟶onto𝐵)
Colors of variables:    wff setvar class
This proof depends on syntax axioms:   → wi 4   ↔ wb 209   ∧ wa 401   ∧ w3a 1103   = wceq 1570  ∃wex 1812   ∈ wcel 2147   ≠ wne 2959  Vcvv 3454   ⊆ wss 3900   ∖ cdif 4048   ∩ cin 4092   ∪ cun 4152  ∅c0 4281  {csn 4588   class class class wbr 5108   × cxp 5656  ◡ccnv 5657  dom cdm 5658  ran crn 5659  Fun wfun 6560   Fn wfn 6561  ⟶wf 6562  ⟶1-1wf1 6563  ⟶ontowfo 6564   ≼ cdom 9009   ≺ csdm 9010  Fincfn 9011
This proof depends on axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1828  ax-4 1842  ax-5 1945  ax-6 2002  ax-7 2043  ax-8 2149  ax-9 2157  ax-10 2180  ax-11 2197  ax-12 2216  ax-ext 2735  ax-sep 5255  ax-nul 5266  ax-pr 5398  ax-un 7783
This proof depends on definitions:  df-bi 210  df-an 402  df-or 862  df-3or 1104  df-3an 1105  df-tru 1573  df-fal 1583  df-ex 1813  df-nf 1817  df-sb 2102  df-mo 2567  df-eu 2597  df-clab 2742  df-cleq 2755  df-clel 2839  df-nfc 2913  df-ne 2960  df-ral 3081  df-rex 3091  df-reu 3370  df-rab 3417  df-v 3456  df-sbc 3743  df-ss 3901  df-pss 4017  df-dif 4050  df-in 4094  df-un 4154  df-nul 4282  df-if 4486  df-pw 4562  df-sn 4589  df-pr 4591  df-op 4841  df-uni 4873  df-br 5109  df-opab 5174  df-mpt 5193  df-tr 5219  df-id 5553  df-eprel 5558  df-po 5566  df-so 5567  df-fr 5611  df-we 5613  df-xp 5664  df-rel 5665  df-cnv 5666  df-co 5667  df-dm 5668  df-rn 5669  df-res 5670  df-ima 5671  df-ord 6391  df-on 6392  df-lim 6393  df-suc 6394  df-iota 6520  df-fun 6568  df-fn 6569  df-f 6570  df-f1 6571  df-fo 6572  df-f1o 6573  df-fv 6574  df-om 7912  df-1o 8514  df-en 9012  df-dom 9013  df-sdom 9014  df-fin 9015
This theorem is used by:  fodomfib  9358
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