Theorem bj-charfunr 15540

Description: If a class 𝐴 has a "weak" characteristic function on a class 𝑋, then negated membership in 𝐴 is decidable (in other words, membership in 𝐴 is testable) in 𝑋.

The hypothesis imposes that 𝑋 be a set. As usual, it could be formulated as ⊢ (𝜑 → (𝐹:𝑋⟶ω ∧ ...)) to deal with general classes, but that extra generality would not make the theorem much more useful.

The theorem would still hold if the codomain of 𝑓 were any class with testable equality to the point where (𝑋 ∖ 𝐴) is sent. (Contributed by BJ, 6-Aug-2024.)

Hypothesis

Ref	Expression
bj-charfunr.1	⊢ (𝜑 → ∃𝑓 ∈ (ω ↑𝑚 𝑋)(∀𝑥 ∈ (𝑋 ∩ 𝐴)(𝑓‘𝑥) ≠ ∅ ∧ ∀𝑥 ∈ (𝑋 ∖ 𝐴)(𝑓‘𝑥) = ∅))

Assertion

Ref	Expression
bj-charfunr	⊢ (𝜑 → ∀𝑥 ∈ 𝑋 DECID ¬ 𝑥 ∈ 𝐴)

Distinct variable groups:   𝐴,𝑓   𝑓,𝑋   𝜑,𝑓,𝑥

Allowed substitution hints:   𝐴(𝑥)   𝑋(𝑥)

Proof of Theorem bj-charfunr

Step	Hyp	Ref	Expression
1		bj-charfunr.1	. . . . 5 ⊢ (𝜑 → ∃𝑓 ∈ (ω ↑𝑚 𝑋)(∀𝑥 ∈ (𝑋 ∩ 𝐴)(𝑓‘𝑥) ≠ ∅ ∧ ∀𝑥 ∈ (𝑋 ∖ 𝐴)(𝑓‘𝑥) = ∅))
2		elmapi 6738	. . . . . . . . . 10 ⊢ (𝑓 ∈ (ω ↑𝑚 𝑋) → 𝑓:𝑋⟶ω)
3		ffvelcdm 5698	. . . . . . . . . . 11 ⊢ ((𝑓:𝑋⟶ω ∧ 𝑥 ∈ 𝑋) → (𝑓‘𝑥) ∈ ω)
4	3	ex 115	. . . . . . . . . 10 ⊢ (𝑓:𝑋⟶ω → (𝑥 ∈ 𝑋 → (𝑓‘𝑥) ∈ ω))
5	2, 4	syl 14	. . . . . . . . 9 ⊢ (𝑓 ∈ (ω ↑𝑚 𝑋) → (𝑥 ∈ 𝑋 → (𝑓‘𝑥) ∈ ω))
6		0elnn 4656	. . . . . . . . . 10 ⊢ ((𝑓‘𝑥) ∈ ω → ((𝑓‘𝑥) = ∅ ∨ ∅ ∈ (𝑓‘𝑥)))
7		nn0eln0 4657	. . . . . . . . . . 11 ⊢ ((𝑓‘𝑥) ∈ ω → (∅ ∈ (𝑓‘𝑥) ↔ (𝑓‘𝑥) ≠ ∅))
8	7	orbi2d 791	. . . . . . . . . 10 ⊢ ((𝑓‘𝑥) ∈ ω → (((𝑓‘𝑥) = ∅ ∨ ∅ ∈ (𝑓‘𝑥)) ↔ ((𝑓‘𝑥) = ∅ ∨ (𝑓‘𝑥) ≠ ∅)))
9	6, 8	mpbid 147	. . . . . . . . 9 ⊢ ((𝑓‘𝑥) ∈ ω → ((𝑓‘𝑥) = ∅ ∨ (𝑓‘𝑥) ≠ ∅))
10	5, 9	syl6 33	. . . . . . . 8 ⊢ (𝑓 ∈ (ω ↑𝑚 𝑋) → (𝑥 ∈ 𝑋 → ((𝑓‘𝑥) = ∅ ∨ (𝑓‘𝑥) ≠ ∅)))
11	10	adantr 276	. . . . . . 7 ⊢ ((𝑓 ∈ (ω ↑𝑚 𝑋) ∧ (∀𝑥 ∈ (𝑋 ∩ 𝐴)(𝑓‘𝑥) ≠ ∅ ∧ ∀𝑥 ∈ (𝑋 ∖ 𝐴)(𝑓‘𝑥) = ∅)) → (𝑥 ∈ 𝑋 → ((𝑓‘𝑥) = ∅ ∨ (𝑓‘𝑥) ≠ ∅)))
12		elin 3347	. . . . . . . . . . . . . . 15 ⊢ (𝑥 ∈ (𝑋 ∩ 𝐴) ↔ (𝑥 ∈ 𝑋 ∧ 𝑥 ∈ 𝐴))
13		rsp 2544	. . . . . . . . . . . . . . 15 ⊢ (∀𝑥 ∈ (𝑋 ∩ 𝐴)(𝑓‘𝑥) ≠ ∅ → (𝑥 ∈ (𝑋 ∩ 𝐴) → (𝑓‘𝑥) ≠ ∅))
14	12, 13	biimtrrid 153	. . . . . . . . . . . . . 14 ⊢ (∀𝑥 ∈ (𝑋 ∩ 𝐴)(𝑓‘𝑥) ≠ ∅ → ((𝑥 ∈ 𝑋 ∧ 𝑥 ∈ 𝐴) → (𝑓‘𝑥) ≠ ∅))
15	14	expd 258	. . . . . . . . . . . . 13 ⊢ (∀𝑥 ∈ (𝑋 ∩ 𝐴)(𝑓‘𝑥) ≠ ∅ → (𝑥 ∈ 𝑋 → (𝑥 ∈ 𝐴 → (𝑓‘𝑥) ≠ ∅)))
16	15	adantr 276	. . . . . . . . . . . 12 ⊢ ((∀𝑥 ∈ (𝑋 ∩ 𝐴)(𝑓‘𝑥) ≠ ∅ ∧ ∀𝑥 ∈ (𝑋 ∖ 𝐴)(𝑓‘𝑥) = ∅) → (𝑥 ∈ 𝑋 → (𝑥 ∈ 𝐴 → (𝑓‘𝑥) ≠ ∅)))
17	16	imp 124	. . . . . . . . . . 11 ⊢ (((∀𝑥 ∈ (𝑋 ∩ 𝐴)(𝑓‘𝑥) ≠ ∅ ∧ ∀𝑥 ∈ (𝑋 ∖ 𝐴)(𝑓‘𝑥) = ∅) ∧ 𝑥 ∈ 𝑋) → (𝑥 ∈ 𝐴 → (𝑓‘𝑥) ≠ ∅))
18	17	necon2bd 2425	. . . . . . . . . 10 ⊢ (((∀𝑥 ∈ (𝑋 ∩ 𝐴)(𝑓‘𝑥) ≠ ∅ ∧ ∀𝑥 ∈ (𝑋 ∖ 𝐴)(𝑓‘𝑥) = ∅) ∧ 𝑥 ∈ 𝑋) → ((𝑓‘𝑥) = ∅ → ¬ 𝑥 ∈ 𝐴))
19		eldif 3166	. . . . . . . . . . . . . . 15 ⊢ (𝑥 ∈ (𝑋 ∖ 𝐴) ↔ (𝑥 ∈ 𝑋 ∧ ¬ 𝑥 ∈ 𝐴))
20		rsp 2544	. . . . . . . . . . . . . . 15 ⊢ (∀𝑥 ∈ (𝑋 ∖ 𝐴)(𝑓‘𝑥) = ∅ → (𝑥 ∈ (𝑋 ∖ 𝐴) → (𝑓‘𝑥) = ∅))
21	19, 20	biimtrrid 153	. . . . . . . . . . . . . 14 ⊢ (∀𝑥 ∈ (𝑋 ∖ 𝐴)(𝑓‘𝑥) = ∅ → ((𝑥 ∈ 𝑋 ∧ ¬ 𝑥 ∈ 𝐴) → (𝑓‘𝑥) = ∅))
22	21	expd 258	. . . . . . . . . . . . 13 ⊢ (∀𝑥 ∈ (𝑋 ∖ 𝐴)(𝑓‘𝑥) = ∅ → (𝑥 ∈ 𝑋 → (¬ 𝑥 ∈ 𝐴 → (𝑓‘𝑥) = ∅)))
23	22	adantl 277	. . . . . . . . . . . 12 ⊢ ((∀𝑥 ∈ (𝑋 ∩ 𝐴)(𝑓‘𝑥) ≠ ∅ ∧ ∀𝑥 ∈ (𝑋 ∖ 𝐴)(𝑓‘𝑥) = ∅) → (𝑥 ∈ 𝑋 → (¬ 𝑥 ∈ 𝐴 → (𝑓‘𝑥) = ∅)))
24	23	imp 124	. . . . . . . . . . 11 ⊢ (((∀𝑥 ∈ (𝑋 ∩ 𝐴)(𝑓‘𝑥) ≠ ∅ ∧ ∀𝑥 ∈ (𝑋 ∖ 𝐴)(𝑓‘𝑥) = ∅) ∧ 𝑥 ∈ 𝑋) → (¬ 𝑥 ∈ 𝐴 → (𝑓‘𝑥) = ∅))
25	24	necon3ad 2409	. . . . . . . . . 10 ⊢ (((∀𝑥 ∈ (𝑋 ∩ 𝐴)(𝑓‘𝑥) ≠ ∅ ∧ ∀𝑥 ∈ (𝑋 ∖ 𝐴)(𝑓‘𝑥) = ∅) ∧ 𝑥 ∈ 𝑋) → ((𝑓‘𝑥) ≠ ∅ → ¬ ¬ 𝑥 ∈ 𝐴))
26	18, 25	orim12d 787	. . . . . . . . 9 ⊢ (((∀𝑥 ∈ (𝑋 ∩ 𝐴)(𝑓‘𝑥) ≠ ∅ ∧ ∀𝑥 ∈ (𝑋 ∖ 𝐴)(𝑓‘𝑥) = ∅) ∧ 𝑥 ∈ 𝑋) → (((𝑓‘𝑥) = ∅ ∨ (𝑓‘𝑥) ≠ ∅) → (¬ 𝑥 ∈ 𝐴 ∨ ¬ ¬ 𝑥 ∈ 𝐴)))
27	26	ex 115	. . . . . . . 8 ⊢ ((∀𝑥 ∈ (𝑋 ∩ 𝐴)(𝑓‘𝑥) ≠ ∅ ∧ ∀𝑥 ∈ (𝑋 ∖ 𝐴)(𝑓‘𝑥) = ∅) → (𝑥 ∈ 𝑋 → (((𝑓‘𝑥) = ∅ ∨ (𝑓‘𝑥) ≠ ∅) → (¬ 𝑥 ∈ 𝐴 ∨ ¬ ¬ 𝑥 ∈ 𝐴))))
28	27	adantl 277	. . . . . . 7 ⊢ ((𝑓 ∈ (ω ↑𝑚 𝑋) ∧ (∀𝑥 ∈ (𝑋 ∩ 𝐴)(𝑓‘𝑥) ≠ ∅ ∧ ∀𝑥 ∈ (𝑋 ∖ 𝐴)(𝑓‘𝑥) = ∅)) → (𝑥 ∈ 𝑋 → (((𝑓‘𝑥) = ∅ ∨ (𝑓‘𝑥) ≠ ∅) → (¬ 𝑥 ∈ 𝐴 ∨ ¬ ¬ 𝑥 ∈ 𝐴))))
29	11, 28	mpdd 41	. . . . . 6 ⊢ ((𝑓 ∈ (ω ↑𝑚 𝑋) ∧ (∀𝑥 ∈ (𝑋 ∩ 𝐴)(𝑓‘𝑥) ≠ ∅ ∧ ∀𝑥 ∈ (𝑋 ∖ 𝐴)(𝑓‘𝑥) = ∅)) → (𝑥 ∈ 𝑋 → (¬ 𝑥 ∈ 𝐴 ∨ ¬ ¬ 𝑥 ∈ 𝐴)))
30	29	adantl 277	. . . . 5 ⊢ ((𝜑 ∧ (𝑓 ∈ (ω ↑𝑚 𝑋) ∧ (∀𝑥 ∈ (𝑋 ∩ 𝐴)(𝑓‘𝑥) ≠ ∅ ∧ ∀𝑥 ∈ (𝑋 ∖ 𝐴)(𝑓‘𝑥) = ∅))) → (𝑥 ∈ 𝑋 → (¬ 𝑥 ∈ 𝐴 ∨ ¬ ¬ 𝑥 ∈ 𝐴)))
31	1, 30	rexlimddv 2619	. . . 4 ⊢ (𝜑 → (𝑥 ∈ 𝑋 → (¬ 𝑥 ∈ 𝐴 ∨ ¬ ¬ 𝑥 ∈ 𝐴)))
32	31	imp 124	. . 3 ⊢ ((𝜑 ∧ 𝑥 ∈ 𝑋) → (¬ 𝑥 ∈ 𝐴 ∨ ¬ ¬ 𝑥 ∈ 𝐴))
33		df-dc 836	. . 3 ⊢ (DECID ¬ 𝑥 ∈ 𝐴 ↔ (¬ 𝑥 ∈ 𝐴 ∨ ¬ ¬ 𝑥 ∈ 𝐴))
34	32, 33	sylibr 134	. 2 ⊢ ((𝜑 ∧ 𝑥 ∈ 𝑋) → DECID ¬ 𝑥 ∈ 𝐴)
35	34	ralrimiva 2570	1 ⊢ (𝜑 → ∀𝑥 ∈ 𝑋 DECID ¬ 𝑥 ∈ 𝐴)

Syntax hints:  ¬ wn 3   → wi 4   ∧ wa 104   ∨ wo 709  DECID wdc 835   = wceq 1364   ∈ wcel 2167   ≠ wne 2367  ∀wral 2475  ∃wrex 2476   ∖ cdif 3154   ∩ cin 3156  ∅c0 3451  ωcom 4627  ⟶wf 5255  ‘cfv 5259  (class class class)co 5925   ↑_𝑚 cmap 6716

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 106  ax-ia2 107  ax-ia3 108  ax-in1 615  ax-in2 616  ax-io 710  ax-5 1461  ax-7 1462  ax-gen 1463  ax-ie1 1507  ax-ie2 1508  ax-8 1518  ax-10 1519  ax-11 1520  ax-i12 1521  ax-bndl 1523  ax-4 1524  ax-17 1540  ax-i9 1544  ax-ial 1548  ax-i5r 1549  ax-13 2169  ax-14 2170  ax-ext 2178  ax-sep 4152  ax-nul 4160  ax-pow 4208  ax-pr 4243  ax-un 4469  ax-setind 4574  ax-iinf 4625

This theorem depends on definitions:  df-bi 117  df-dc 836  df-3an 982  df-tru 1367  df-fal 1370  df-nf 1475  df-sb 1777  df-eu 2048  df-mo 2049  df-clab 2183  df-cleq 2189  df-clel 2192  df-nfc 2328  df-ne 2368  df-ral 2480  df-rex 2481  df-v 2765  df-sbc 2990  df-dif 3159  df-un 3161  df-in 3163  df-ss 3170  df-nul 3452  df-pw 3608  df-sn 3629  df-pr 3630  df-op 3632  df-uni 3841  df-int 3876  df-br 4035  df-opab 4096  df-id 4329  df-suc 4407  df-iom 4628  df-xp 4670  df-rel 4671  df-cnv 4672  df-co 4673  df-dm 4674  df-rn 4675  df-iota 5220  df-fun 5261  df-fn 5262  df-f 5263  df-fv 5267  df-ov 5928  df-oprab 5929  df-mpo 5930  df-map 6718

This theorem is referenced by:  bj-charfunbi  15541