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Theorem fodomfir 9326
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 9154). (Contributed by BTernaryTau, 23-Jun-2025.)
Assertion
Ref Expression
fodomfir ((𝐴 ∈ Fin ∧ ∅ ≺ 𝐵 ∧ 𝐵 ≼ 𝐴) → ∃𝑓 𝑓:𝐴–onto→𝐵)
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 8987 . . . . . . 7 Rel ≺
21brrelex2i 5708 . . . . . 6 (∅ ≺ 𝐵 → 𝐵 ∈ V)
3 0sdomg 9132 . . . . . . 7 (𝐵 ∈ V → (∅ ≺ 𝐵 ↔ 𝐵 ≠ ∅))
4 n0 4299 . . . . . . 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 9211 . . . . . 6 ((𝐴 ∈ Fin ∧ 𝐵 ≼ 𝐴) → 𝐵 ∈ Fin)
9 simpl 488 . . . . . 6 ((𝐴 ∈ Fin ∧ 𝐵 ≼ 𝐴) → 𝐴 ∈ Fin)
10 brdomi 8993 . . . . . . . 8 (𝐵 ≼ 𝐴 → ∃𝑔 𝑔:𝐵–1-1→𝐴)
11 f1fn 6784 . . . . . . . . . . . 12 (𝑔:𝐵–1-1→𝐴 → 𝑔 Fn 𝐵)
12 fnfi 9200 . . . . . . . . . . . 12 ((𝑔 Fn 𝐵 ∧ 𝐵 ∈ Fin) → 𝑔 ∈ Fin)
1311, 12sylan 592 . . . . . . . . . . 11 ((𝑔:𝐵–1-1→𝐴 ∧ 𝐵 ∈ Fin) → 𝑔 ∈ Fin)
1413ex 418 . . . . . . . . . 10 (𝑔:𝐵–1-1→𝐴 → (𝐵 ∈ Fin → 𝑔 ∈ Fin))
15 cnvfi 9198 . . . . . . . . . . . . . 14 (𝑔 ∈ Fin → ◡𝑔 ∈ Fin)
16 diffi 9197 . . . . . . . . . . . . . . 15 (𝐴 ∈ Fin → (𝐴 ∖ ran 𝑔) ∈ Fin)
17 snfi 9078 . . . . . . . . . . . . . . 15 {𝑧} ∈ Fin
18 xpfi 9318 . . . . . . . . . . . . . . 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 9193 . . . . . . . . . . . . . 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 6548 . . . . . . . . . . . . . . . . . . 19 (𝑔:𝐵–1-1→𝐴 ↔ (𝑔:𝐵⟶𝐴 ∧ Fun ◡𝑔))
2322simprbi 503 . . . . . . . . . . . . . . . . . 18 (𝑔:𝐵–1-1→𝐴 → Fun ◡𝑔)
24 vex 3454 . . . . . . . . . . . . . . . . . . . 20 𝑧 ∈ V
2524fconst 6773 . . . . . . . . . . . . . . . . . . 19 ((𝐴 ∖ ran 𝑔) × {𝑧}):(𝐴 ∖ ran 𝑔)⟶{𝑧}
26 ffun 6717 . . . . . . . . . . . . . . . . . . 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–1-1→𝐴 → (Fun ◡𝑔 ∧ Fun ((𝐴 ∖ ran 𝑔) × {𝑧})))
29 df-rn 5662 . . . . . . . . . . . . . . . . . . . 20 ran 𝑔 = dom ◡𝑔
3029eqcomi 2769 . . . . . . . . . . . . . . . . . . 19 dom ◡𝑔 = ran 𝑔
3124snnz 4733 . . . . . . . . . . . . . . . . . . . 20 {𝑧} ≠ ∅
32 dmxp 5912 . . . . . . . . . . . . . . . . . . . 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 4114 . . . . . . . . . . . . . . . . . 18 (dom ◡𝑔 ∩ dom ((𝐴 ∖ ran 𝑔) × {𝑧})) = (ran 𝑔 ∩ (𝐴 ∖ ran 𝑔))
35 disjdif 4425 . . . . . . . . . . . . . . . . . 18 (ran 𝑔 ∩ (𝐴 ∖ ran 𝑔)) = ∅
3634, 35eqtri 2783 . . . . . . . . . . . . . . . . 17 (dom ◡𝑔 ∩ dom ((𝐴 ∖ ran 𝑔) × {𝑧})) = ∅
37 funun 6591 . . . . . . . . . . . . . . . . 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–1-1→𝐴 → Fun (◡𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})))
3938adantl 487 . . . . . . . . . . . . . . 15 ((𝑧 ∈ 𝐵 ∧ 𝑔:𝐵–1-1→𝐴) → Fun (◡𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})))
40 dmun 5893 . . . . . . . . . . . . . . . . . 18 dom (◡𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) = (dom ◡𝑔 ∪ dom ((𝐴 ∖ ran 𝑔) × {𝑧}))
4129uneq1i 4162 . . . . . . . . . . . . . . . . . 18 (ran 𝑔 ∪ dom ((𝐴 ∖ ran 𝑔) × {𝑧})) = (dom ◡𝑔 ∪ dom ((𝐴 ∖ ran 𝑔) × {𝑧}))
4233uneq2i 4163 . . . . . . . . . . . . . . . . . 18 (ran 𝑔 ∪ dom ((𝐴 ∖ ran 𝑔) × {𝑧})) = (ran 𝑔 ∪ (𝐴 ∖ ran 𝑔))
4340, 41, 423eqtr2i 2789 . . . . . . . . . . . . . . . . 17 dom (◡𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) = (ran 𝑔 ∪ (𝐴 ∖ ran 𝑔))
44 f1f 6783 . . . . . . . . . . . . . . . . . . 19 (𝑔:𝐵–1-1→𝐴 → 𝑔:𝐵⟶𝐴)
4544frnd 6723 . . . . . . . . . . . . . . . . . 18 (𝑔:𝐵–1-1→𝐴 → ran 𝑔 ⊆ 𝐴)
46 undif 4437 . . . . . . . . . . . . . . . . . 18 (ran 𝑔 ⊆ 𝐴 ↔ (ran 𝑔 ∪ (𝐴 ∖ ran 𝑔)) = 𝐴)
4745, 46sylib 221 . . . . . . . . . . . . . . . . 17 (𝑔:𝐵–1-1→𝐴 → (ran 𝑔 ∪ (𝐴 ∖ ran 𝑔)) = 𝐴)
4843, 47eqtrid 2807 . . . . . . . . . . . . . . . 16 (𝑔:𝐵–1-1→𝐴 → dom (◡𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) = 𝐴)
4948adantl 487 . . . . . . . . . . . . . . 15 ((𝑧 ∈ 𝐵 ∧ 𝑔:𝐵–1-1→𝐴) → dom (◡𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) = 𝐴)
50 df-fn 6546 . . . . . . . . . . . . . . 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–1-1→𝐴) → (◡𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) Fn 𝐴)
52 rnun 6138 . . . . . . . . . . . . . . 15 ran (◡𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) = (ran ◡𝑔 ∪ ran ((𝐴 ∖ ran 𝑔) × {𝑧}))
53 dfdm4 5878 . . . . . . . . . . . . . . . . . 18 dom 𝑔 = ran ◡𝑔
54 f1dm 6789 . . . . . . . . . . . . . . . . . 18 (𝑔:𝐵–1-1→𝐴 → dom 𝑔 = 𝐵)
5553, 54eqtr3id 2809 . . . . . . . . . . . . . . . . 17 (𝑔:𝐵–1-1→𝐴 → ran ◡𝑔 = 𝐵)
5655uneq1d 4165 . . . . . . . . . . . . . . . 16 (𝑔:𝐵–1-1→𝐴 → (ran ◡𝑔 ∪ ran ((𝐴 ∖ ran 𝑔) × {𝑧})) = (𝐵 ∪ ran ((𝐴 ∖ ran 𝑔) × {𝑧})))
57 xpeq1 5665 . . . . . . . . . . . . . . . . . . . . . . 23 ((𝐴 ∖ ran 𝑔) = ∅ → ((𝐴 ∖ ran 𝑔) × {𝑧}) = (∅ × {𝑧}))
58 0xp 5751 . . . . . . . . . . . . . . . . . . . . . . 23 (∅ × {𝑧}) = ∅
5957, 58eqtrdi 2811 . . . . . . . . . . . . . . . . . . . . . 22 ((𝐴 ∖ ran 𝑔) = ∅ → ((𝐴 ∖ ran 𝑔) × {𝑧}) = ∅)
6059rneqd 5921 . . . . . . . . . . . . . . . . . . . . 21 ((𝐴 ∖ ran 𝑔) = ∅ → ran ((𝐴 ∖ ran 𝑔) × {𝑧}) = ran ∅)
61 rn0 5909 . . . . . . . . . . . . . . . . . . . . 21 ran ∅ = ∅
6260, 61eqtrdi 2811 . . . . . . . . . . . . . . . . . . . 20 ((𝐴 ∖ ran 𝑔) = ∅ → ran ((𝐴 ∖ ran 𝑔) × {𝑧}) = ∅)
63 0ss 4349 . . . . . . . . . . . . . . . . . . . 20 ∅ ⊆ 𝐵
6462, 63eqsstrdi 3953 . . . . . . . . . . . . . . . . . . 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 6164 . . . . . . . . . . . . . . . . . . . . 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 4742 . . . . . . . . . . . . . . . . . . . . 21 (𝑧 ∈ 𝐵 → {𝑧} ⊆ 𝐵)
6968adantl 487 . . . . . . . . . . . . . . . . . . . 20 (((𝐴 ∖ ran 𝑔) ≠ ∅ ∧ 𝑧 ∈ 𝐵) → {𝑧} ⊆ 𝐵)
7067, 69eqsstrd 3943 . . . . . . . . . . . . . . . . . . 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 3038 . . . . . . . . . . . . . . . . 17 (𝑧 ∈ 𝐵 → ran ((𝐴 ∖ ran 𝑔) × {𝑧}) ⊆ 𝐵)
73 ssequn2 4186 . . . . . . . . . . . . . . . . 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 2817 . . . . . . . . . . . . . . 15 ((𝑧 ∈ 𝐵 ∧ 𝑔:𝐵–1-1→𝐴) → (ran ◡𝑔 ∪ ran ((𝐴 ∖ ran 𝑔) × {𝑧})) = 𝐵)
7652, 75eqtrid 2807 . . . . . . . . . . . . . 14 ((𝑧 ∈ 𝐵 ∧ 𝑔:𝐵–1-1→𝐴) → ran (◡𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) = 𝐵)
77 df-fo 6549 . . . . . . . . . . . . . 14 ((◡𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})):𝐴–onto→𝐵 ↔ ((◡𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) Fn 𝐴 ∧ ran (◡𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) = 𝐵))
7851, 76, 77sylanbrc 595 . . . . . . . . . . . . 13 ((𝑧 ∈ 𝐵 ∧ 𝑔:𝐵–1-1→𝐴) → (◡𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})):𝐴–onto→𝐵)
79 foeq1 6797 . . . . . . . . . . . . . 14 (𝑓 = (◡𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) → (𝑓:𝐴–onto→𝐵 ↔ (◡𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})):𝐴–onto→𝐵))
8079spcegv 3551 . . . . . . . . . . . . 13 ((◡𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})) ∈ Fin → ((◡𝑔 ∪ ((𝐴 ∖ ran 𝑔) × {𝑧})):𝐴–onto→𝐵 → ∃𝑓 𝑓:𝐴–onto→𝐵))
8121, 78, 80syl2im 41 . . . . . . . . . . . 12 ((𝑔 ∈ Fin ∧ 𝐴 ∈ Fin) → ((𝑧 ∈ 𝐵 ∧ 𝑔:𝐵–1-1→𝐴) → ∃𝑓 𝑓:𝐴–onto→𝐵))
8281expcomd 422 . . . . . . . . . . 11 ((𝑔 ∈ Fin ∧ 𝐴 ∈ Fin) → (𝑔:𝐵–1-1→𝐴 → (𝑧 ∈ 𝐵 → ∃𝑓 𝑓:𝐴–onto→𝐵)))
8382com12 33 . . . . . . . . . 10 (𝑔:𝐵–1-1→𝐴 → ((𝑔 ∈ Fin ∧ 𝐴 ∈ Fin) → (𝑧 ∈ 𝐵 → ∃𝑓 𝑓:𝐴–onto→𝐵)))
8414, 83syland 615 . . . . . . . . 9 (𝑔:𝐵–1-1→𝐴 → ((𝐵 ∈ Fin ∧ 𝐴 ∈ Fin) → (𝑧 ∈ 𝐵 → ∃𝑓 𝑓:𝐴–onto→𝐵)))
8584exlimiv 1962 . . . . . . . 8 (∃𝑔 𝑔:𝐵–1-1→𝐴 → ((𝐵 ∈ Fin ∧ 𝐴 ∈ Fin) → (𝑧 ∈ 𝐵 → ∃𝑓 𝑓:𝐴–onto→𝐵)))
8610, 85syl 18 . . . . . . 7 (𝐵 ≼ 𝐴 → ((𝐵 ∈ Fin ∧ 𝐴 ∈ Fin) → (𝑧 ∈ 𝐵 → ∃𝑓 𝑓:𝐴–onto→𝐵)))
8786adantl 487 . . . . . 6 ((𝐴 ∈ Fin ∧ 𝐵 ≼ 𝐴) → ((𝐵 ∈ Fin ∧ 𝐴 ∈ Fin) → (𝑧 ∈ 𝐵 → ∃𝑓 𝑓:𝐴–onto→𝐵)))
888, 9, 87mp2and 712 . . . . 5 ((𝐴 ∈ Fin ∧ 𝐵 ≼ 𝐴) → (𝑧 ∈ 𝐵 → ∃𝑓 𝑓:𝐴–onto→𝐵))
8988exlimdv 1965 . . . 4 ((𝐴 ∈ Fin ∧ 𝐵 ≼ 𝐴) → (∃𝑧 𝑧 ∈ 𝐵 → ∃𝑓 𝑓:𝐴–onto→𝐵))
907, 89syl5 35 . . 3 ((𝐴 ∈ Fin ∧ 𝐵 ≼ 𝐴) → (∅ ≺ 𝐵 → ∃𝑓 𝑓:𝐴–onto→𝐵))
91903impia 1135 . 2 ((𝐴 ∈ Fin ∧ 𝐵 ≼ 𝐴 ∧ ∅ ≺ 𝐵) → ∃𝑓 𝑓:𝐴–onto→𝐵)
92913com23 1144 1 ((𝐴 ∈ Fin ∧ ∅ ≺ 𝐵 ∧ 𝐵 ≼ 𝐴) → ∃𝑓 𝑓:𝐴–onto→𝐵)
Colors of variables:    wff setvar class
This proof depends on syntax axioms:   → wi 4   ↔ wb 209   ∧ wa 401   ∧ w3a 1103   = wceq 1569  ∃wex 1811   ∈ wcel 2144   ≠ wne 2955  Vcvv 3450   ⊆ wss 3896   ∖ cdif 4044   ∩ cin 4088   ∪ cun 4148  ∅c0 4277  {csn 4584   class class class wbr 5102   × cxp 5649  ◡ccnv 5650  dom cdm 5651  ran crn 5652  Fun wfun 6537   Fn wfn 6538  ⟶wf 6539  –1-1→wf1 6540  –onto→wfo 6541   ≼ cdom 8978   ≺ csdm 8979  Fincfn 8980
This proof depends on axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1827  ax-4 1841  ax-5 1942  ax-6 1999  ax-7 2040  ax-8 2146  ax-9 2154  ax-10 2177  ax-11 2193  ax-12 2212  ax-ext 2732  ax-sep 5248  ax-nul 5259  ax-pr 5391  ax-un 7755
This proof depends on definitions:  df-bi 210  df-an 402  df-or 862  df-3or 1104  df-3an 1105  df-tru 1572  df-fal 1582  df-ex 1812  df-nf 1816  df-sb 2099  df-mo 2564  df-eu 2594  df-clab 2739  df-cleq 2752  df-clel 2835  df-nfc 2909  df-ne 2956  df-ral 3077  df-rex 3087  df-reu 3366  df-rab 3413  df-v 3452  df-sbc 3739  df-ss 3897  df-pss 4013  df-dif 4046  df-in 4090  df-un 4150  df-nul 4278  df-if 4482  df-pw 4558  df-sn 4585  df-pr 4587  df-op 4835  df-uni 4867  df-br 5103  df-opab 5167  df-mpt 5186  df-tr 5212  df-id 5546  df-eprel 5551  df-po 5559  df-so 5560  df-fr 5604  df-we 5606  df-xp 5657  df-rel 5658  df-cnv 5659  df-co 5660  df-dm 5661  df-rn 5662  df-res 5663  df-ima 5664  df-ord 6368  df-on 6369  df-lim 6370  df-suc 6371  df-iota 6497  df-fun 6545  df-fn 6546  df-f 6547  df-f1 6548  df-fo 6549  df-f1o 6550  df-fv 6551  df-om 7882  df-1o 8483  df-en 8981  df-dom 8982  df-sdom 8983  df-fin 8984
This theorem is used by:  fodomfib  9327
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