Theorem dmct 10606

Description: The domain of a countable set is countable. The proof uses fodomnum 10140 rather than fodomg 10604, and so does not require ax-ac 10541. (Contributed by Thierry Arnoux, 29-Dec-2016.) (Revised by Vincent Gonzalez, 24-Aug-2026.)

Assertion

Ref	Expression
dmct	⊢ (𝐴 ≼ ω → dom 𝐴 ≼ ω)

Proof of Theorem dmct

Dummy variable 𝑥 is distinct from all other variables.

Step	Hyp	Ref	Expression
1		dmresv 6194	. 2 ⊢ dom (𝐴 ↾ V) = dom 𝐴
2		omelon 9651	. . . . . . 7 ⊢ ω ∈ On
3	2	a1i 11	. . . . . 6 ⊢ (𝐴 ≼ ω → ω ∈ On)
4		id 23	. . . . . 6 ⊢ (𝐴 ≼ ω → 𝐴 ≼ ω)
5		ondomen 10120	. . . . . 6 ⊢ ((ω ∈ On ∧ 𝐴 ≼ ω) → 𝐴 ∈ dom card)
6	3, 4, 5	syl2anc 596	. . . . 5 ⊢ (𝐴 ≼ ω → 𝐴 ∈ dom card)
7		resss 5991	. . . . . 6 ⊢ (𝐴 ↾ V) ⊆ 𝐴
8	7	a1i 11	. . . . 5 ⊢ (𝐴 ≼ ω → (𝐴 ↾ V) ⊆ 𝐴)
9		ssnum 10122	. . . . 5 ⊢ ((𝐴 ∈ dom card ∧ (𝐴 ↾ V) ⊆ 𝐴) → (𝐴 ↾ V) ∈ dom card)
10	6, 8, 9	syl2anc 596	. . . 4 ⊢ (𝐴 ≼ ω → (𝐴 ↾ V) ∈ dom card)
11		fvex 6899	. . . . . . 7 ⊢ (1st ‘𝑥) ∈ V
12		eqid 2760	. . . . . . 7 ⊢ (𝑥 ∈ (𝐴 ↾ V) ↦ (1st ‘𝑥)) = (𝑥 ∈ (𝐴 ↾ V) ↦ (1st ‘𝑥))
13	11, 12	fnmpti 6683	. . . . . 6 ⊢ (𝑥 ∈ (𝐴 ↾ V) ↦ (1st ‘𝑥)) Fn (𝐴 ↾ V)
14		dffn4 6803	. . . . . 6 ⊢ ((𝑥 ∈ (𝐴 ↾ V) ↦ (1st ‘𝑥)) Fn (𝐴 ↾ V) ↔ (𝑥 ∈ (𝐴 ↾ V) ↦ (1st ‘𝑥)):(𝐴 ↾ V)–onto→ran (𝑥 ∈ (𝐴 ↾ V) ↦ (1st ‘𝑥)))
15	13, 14	mpbi 233	. . . . 5 ⊢ (𝑥 ∈ (𝐴 ↾ V) ↦ (1st ‘𝑥)):(𝐴 ↾ V)–onto→ran (𝑥 ∈ (𝐴 ↾ V) ↦ (1st ‘𝑥))
16		relres 5995	. . . . . 6 ⊢ Rel (𝐴 ↾ V)
17		reldm 8056	. . . . . 6 ⊢ (Rel (𝐴 ↾ V) → dom (𝐴 ↾ V) = ran (𝑥 ∈ (𝐴 ↾ V) ↦ (1st ‘𝑥)))
18		foeq3 6795	. . . . . 6 ⊢ (dom (𝐴 ↾ V) = ran (𝑥 ∈ (𝐴 ↾ V) ↦ (1st ‘𝑥)) → ((𝑥 ∈ (𝐴 ↾ V) ↦ (1st ‘𝑥)):(𝐴 ↾ V)–onto→dom (𝐴 ↾ V) ↔ (𝑥 ∈ (𝐴 ↾ V) ↦ (1st ‘𝑥)):(𝐴 ↾ V)–onto→ran (𝑥 ∈ (𝐴 ↾ V) ↦ (1st ‘𝑥))))
19	16, 17, 18	mp2b 10	. . . . 5 ⊢ ((𝑥 ∈ (𝐴 ↾ V) ↦ (1st ‘𝑥)):(𝐴 ↾ V)–onto→dom (𝐴 ↾ V) ↔ (𝑥 ∈ (𝐴 ↾ V) ↦ (1st ‘𝑥)):(𝐴 ↾ V)–onto→ran (𝑥 ∈ (𝐴 ↾ V) ↦ (1st ‘𝑥)))
20	15, 19	mpbir 234	. . . 4 ⊢ (𝑥 ∈ (𝐴 ↾ V) ↦ (1st ‘𝑥)):(𝐴 ↾ V)–onto→dom (𝐴 ↾ V)
21		fodomnum 10140	. . . 4 ⊢ ((𝐴 ↾ V) ∈ dom card → ((𝑥 ∈ (𝐴 ↾ V) ↦ (1st ‘𝑥)):(𝐴 ↾ V)–onto→dom (𝐴 ↾ V) → dom (𝐴 ↾ V) ≼ (𝐴 ↾ V)))
22	10, 20, 21	mpisyl 22	. . 3 ⊢ (𝐴 ≼ ω → dom (𝐴 ↾ V) ≼ (𝐴 ↾ V))
23		ctex 8994	. . . . 5 ⊢ (𝐴 ≼ ω → 𝐴 ∈ V)
24		ssdomg 9031	. . . . 5 ⊢ (𝐴 ∈ V → ((𝐴 ↾ V) ⊆ 𝐴 → (𝐴 ↾ V) ≼ 𝐴))
25	23, 7, 24	mpisyl 22	. . . 4 ⊢ (𝐴 ≼ ω → (𝐴 ↾ V) ≼ 𝐴)
26		domtr 9038	. . . 4 ⊢ (((𝐴 ↾ V) ≼ 𝐴 ∧ 𝐴 ≼ ω) → (𝐴 ↾ V) ≼ ω)
27	25, 26	mpancom 701	. . 3 ⊢ (𝐴 ≼ ω → (𝐴 ↾ V) ≼ ω)
28		domtr 9038	. . 3 ⊢ ((dom (𝐴 ↾ V) ≼ (𝐴 ↾ V) ∧ (𝐴 ↾ V) ≼ ω) → dom (𝐴 ↾ V) ≼ ω)
29	22, 27, 28	syl2anc 596	. 2 ⊢ (𝐴 ≼ ω → dom (𝐴 ↾ V) ≼ ω)
30	1, 29	eqbrtrrid 5140	1 ⊢ (𝐴 ≼ ω → dom 𝐴 ≼ ω)

This proof depends on syntax axioms:   → wi 4   ↔ wb 209   = wceq 1569   ∈ wcel 2144  Vcvv 3450   ⊆ wss 3895   class class class wbr 5102   ↦ cmpt 5185  dom cdm 5650  ran crn 5651   ↾ cres 5652  Rel wrel 5655  Oncon0 6362   Fn wfn 6534  –onto→wfo 6537  ‘cfv 6539  ωcom 7878  1^st c1st 8000   ≼ cdom 8975  cardccrd 10020

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-rep 5231  ax-sep 5248  ax-nul 5259  ax-pow 5326  ax-pr 5390  ax-un 7752  ax-inf2 9646

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-rmo 3365  df-reu 3366  df-rab 3413  df-v 3452  df-sbc 3739  df-csb 3847  df-ss 3896  df-pss 4014  df-dif 4047  df-in 4091  df-un 4151  df-nul 4279  df-if 4482  df-pw 4558  df-sn 4585  df-pr 4587  df-op 4835  df-uni 4867  df-int 4907  df-iun 4952  df-br 5103  df-opab 5167  df-mpt 5186  df-tr 5212  df-id 5545  df-eprel 5550  df-po 5558  df-so 5559  df-fr 5603  df-se 5604  df-we 5605  df-xp 5656  df-rel 5657  df-cnv 5658  df-co 5659  df-dm 5660  df-rn 5661  df-res 5662  df-ima 5663  df-pred 6304  df-ord 6365  df-on 6366  df-lim 6367  df-suc 6368  df-iota 6494  df-fun 6541  df-fn 6542  df-f 6543  df-f1 6544  df-fo 6545  df-f1o 6546  df-fv 6547  df-isom 6548  df-riota 7378  df-ov 7424  df-oprab 7425  df-mpo 7426  df-om 7879  df-1st 8002  df-2nd 8003  df-frecs 8303  df-wrecs 8334  df-recs 8383  df-er 8721  df-map 8853  df-en 8978  df-dom 8979  df-card 10024  df-acn 10027

This theorem is used by:  rnct  10608