Theorem 4sqexercise2 13201

Description: Exercise which may help in understanding the proof of 4sqlemsdc 13202. (Contributed by Jim Kingdon, 30-May-2025.)

Hypothesis

Ref	Expression
4sqexercise2.s	⊢ 𝑆 = {𝑛 ∣ ∃𝑥 ∈ ℤ ∃𝑦 ∈ ℤ 𝑛 = ((𝑥↑2) + (𝑦↑2))}

Assertion

Ref	Expression
4sqexercise2	⊢ (𝐴 ∈ ℕ0 → DECID 𝐴 ∈ 𝑆)

Distinct variable group:   𝐴,𝑛,𝑥,𝑦

Allowed substitution hints:   𝑆(𝑥, 𝑦, 𝑛)

Proof of Theorem 4sqexercise2

Step	Hyp	Ref	Expression
1		nn0negz 9683	. . . 4 ⊢ (𝐴 ∈ ℕ0 → -𝐴 ∈ ℤ)
2		nn0z 9669	. . . 4 ⊢ (𝐴 ∈ ℕ0 → 𝐴 ∈ ℤ)
3	1	adantr 276	. . . . . 6 ⊢ ((𝐴 ∈ ℕ0 ∧ 𝑥 ∈ (-𝐴...𝐴)) → -𝐴 ∈ ℤ)
4	2	adantr 276	. . . . . 6 ⊢ ((𝐴 ∈ ℕ0 ∧ 𝑥 ∈ (-𝐴...𝐴)) → 𝐴 ∈ ℤ)
5	4	adantr 276	. . . . . . 7 ⊢ (((𝐴 ∈ ℕ0 ∧ 𝑥 ∈ (-𝐴...𝐴)) ∧ 𝑦 ∈ (-𝐴...𝐴)) → 𝐴 ∈ ℤ)
6		elfzelz 10439	. . . . . . . . . 10 ⊢ (𝑥 ∈ (-𝐴...𝐴) → 𝑥 ∈ ℤ)
7	6	ad2antlr 493	. . . . . . . . 9 ⊢ (((𝐴 ∈ ℕ0 ∧ 𝑥 ∈ (-𝐴...𝐴)) ∧ 𝑦 ∈ (-𝐴...𝐴)) → 𝑥 ∈ ℤ)
8		zsqcl 11062	. . . . . . . . 9 ⊢ (𝑥 ∈ ℤ → (𝑥↑2) ∈ ℤ)
9	7, 8	syl 14	. . . . . . . 8 ⊢ (((𝐴 ∈ ℕ0 ∧ 𝑥 ∈ (-𝐴...𝐴)) ∧ 𝑦 ∈ (-𝐴...𝐴)) → (𝑥↑2) ∈ ℤ)
10		elfzelz 10439	. . . . . . . . . 10 ⊢ (𝑦 ∈ (-𝐴...𝐴) → 𝑦 ∈ ℤ)
11	10	adantl 277	. . . . . . . . 9 ⊢ (((𝐴 ∈ ℕ0 ∧ 𝑥 ∈ (-𝐴...𝐴)) ∧ 𝑦 ∈ (-𝐴...𝐴)) → 𝑦 ∈ ℤ)
12		zsqcl 11062	. . . . . . . . 9 ⊢ (𝑦 ∈ ℤ → (𝑦↑2) ∈ ℤ)
13	11, 12	syl 14	. . . . . . . 8 ⊢ (((𝐴 ∈ ℕ0 ∧ 𝑥 ∈ (-𝐴...𝐴)) ∧ 𝑦 ∈ (-𝐴...𝐴)) → (𝑦↑2) ∈ ℤ)
14	9, 13	zaddcld 9777	. . . . . . 7 ⊢ (((𝐴 ∈ ℕ0 ∧ 𝑥 ∈ (-𝐴...𝐴)) ∧ 𝑦 ∈ (-𝐴...𝐴)) → ((𝑥↑2) + (𝑦↑2)) ∈ ℤ)
15		zdceq 9725	. . . . . . 7 ⊢ ((𝐴 ∈ ℤ ∧ ((𝑥↑2) + (𝑦↑2)) ∈ ℤ) → DECID 𝐴 = ((𝑥↑2) + (𝑦↑2)))
16	5, 14, 15	syl2anc 415	. . . . . 6 ⊢ (((𝐴 ∈ ℕ0 ∧ 𝑥 ∈ (-𝐴...𝐴)) ∧ 𝑦 ∈ (-𝐴...𝐴)) → DECID 𝐴 = ((𝑥↑2) + (𝑦↑2)))
17	3, 4, 16	exfzdc 10670	. . . . 5 ⊢ ((𝐴 ∈ ℕ0 ∧ 𝑥 ∈ (-𝐴...𝐴)) → DECID ∃𝑦 ∈ (-𝐴...𝐴)𝐴 = ((𝑥↑2) + (𝑦↑2)))
18	3	adantr 276	. . . . . . . . . . 11 ⊢ (((𝐴 ∈ ℕ0 ∧ 𝑥 ∈ (-𝐴...𝐴)) ∧ (𝑦 ∈ ℤ ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2)))) → -𝐴 ∈ ℤ)
19	4	adantr 276	. . . . . . . . . . 11 ⊢ (((𝐴 ∈ ℕ0 ∧ 𝑥 ∈ (-𝐴...𝐴)) ∧ (𝑦 ∈ ℤ ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2)))) → 𝐴 ∈ ℤ)
20		simprl 535	. . . . . . . . . . 11 ⊢ (((𝐴 ∈ ℕ0 ∧ 𝑥 ∈ (-𝐴...𝐴)) ∧ (𝑦 ∈ ℤ ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2)))) → 𝑦 ∈ ℤ)
21	20	zred 9773	. . . . . . . . . . . 12 ⊢ (((𝐴 ∈ ℕ0 ∧ 𝑥 ∈ (-𝐴...𝐴)) ∧ (𝑦 ∈ ℤ ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2)))) → 𝑦 ∈ ℝ)
22	19	zred 9773	. . . . . . . . . . . 12 ⊢ (((𝐴 ∈ ℕ0 ∧ 𝑥 ∈ (-𝐴...𝐴)) ∧ (𝑦 ∈ ℤ ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2)))) → 𝐴 ∈ ℝ)
23	21	renegcld 8709	. . . . . . . . . . . . 13 ⊢ (((𝐴 ∈ ℕ0 ∧ 𝑥 ∈ (-𝐴...𝐴)) ∧ (𝑦 ∈ ℤ ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2)))) → -𝑦 ∈ ℝ)
24		zsqcl2 11069	. . . . . . . . . . . . . . 15 ⊢ (𝑦 ∈ ℤ → (𝑦↑2) ∈ ℕ0)
25	20, 24	syl 14	. . . . . . . . . . . . . 14 ⊢ (((𝐴 ∈ ℕ0 ∧ 𝑥 ∈ (-𝐴...𝐴)) ∧ (𝑦 ∈ ℤ ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2)))) → (𝑦↑2) ∈ ℕ0)
26	25	nn0red 9626	. . . . . . . . . . . . 13 ⊢ (((𝐴 ∈ ℕ0 ∧ 𝑥 ∈ (-𝐴...𝐴)) ∧ (𝑦 ∈ ℤ ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2)))) → (𝑦↑2) ∈ ℝ)
27		znegcl 9680	. . . . . . . . . . . . . . . 16 ⊢ (𝑦 ∈ ℤ → -𝑦 ∈ ℤ)
28		zzlesq 11161	. . . . . . . . . . . . . . . 16 ⊢ (-𝑦 ∈ ℤ → -𝑦 ≤ (-𝑦↑2))
29	27, 28	syl 14	. . . . . . . . . . . . . . 15 ⊢ (𝑦 ∈ ℤ → -𝑦 ≤ (-𝑦↑2))
30		zcn 9654	. . . . . . . . . . . . . . . 16 ⊢ (𝑦 ∈ ℤ → 𝑦 ∈ ℂ)
31		sqneg 11050	. . . . . . . . . . . . . . . 16 ⊢ (𝑦 ∈ ℂ → (-𝑦↑2) = (𝑦↑2))
32	30, 31	syl 14	. . . . . . . . . . . . . . 15 ⊢ (𝑦 ∈ ℤ → (-𝑦↑2) = (𝑦↑2))
33	29, 32	breqtrd 4156	. . . . . . . . . . . . . 14 ⊢ (𝑦 ∈ ℤ → -𝑦 ≤ (𝑦↑2))
34	20, 33	syl 14	. . . . . . . . . . . . 13 ⊢ (((𝐴 ∈ ℕ0 ∧ 𝑥 ∈ (-𝐴...𝐴)) ∧ (𝑦 ∈ ℤ ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2)))) → -𝑦 ≤ (𝑦↑2))
35	6	ad2antlr 493	. . . . . . . . . . . . . . . 16 ⊢ (((𝐴 ∈ ℕ0 ∧ 𝑥 ∈ (-𝐴...𝐴)) ∧ (𝑦 ∈ ℤ ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2)))) → 𝑥 ∈ ℤ)
36		zsqcl2 11069	. . . . . . . . . . . . . . . 16 ⊢ (𝑥 ∈ ℤ → (𝑥↑2) ∈ ℕ0)
37	35, 36	syl 14	. . . . . . . . . . . . . . 15 ⊢ (((𝐴 ∈ ℕ0 ∧ 𝑥 ∈ (-𝐴...𝐴)) ∧ (𝑦 ∈ ℤ ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2)))) → (𝑥↑2) ∈ ℕ0)
38		nn0addge2 9615	. . . . . . . . . . . . . . 15 ⊢ (((𝑦↑2) ∈ ℝ ∧ (𝑥↑2) ∈ ℕ0) → (𝑦↑2) ≤ ((𝑥↑2) + (𝑦↑2)))
39	26, 37, 38	syl2anc 415	. . . . . . . . . . . . . 14 ⊢ (((𝐴 ∈ ℕ0 ∧ 𝑥 ∈ (-𝐴...𝐴)) ∧ (𝑦 ∈ ℤ ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2)))) → (𝑦↑2) ≤ ((𝑥↑2) + (𝑦↑2)))
40		simprr 537	. . . . . . . . . . . . . 14 ⊢ (((𝐴 ∈ ℕ0 ∧ 𝑥 ∈ (-𝐴...𝐴)) ∧ (𝑦 ∈ ℤ ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2)))) → 𝐴 = ((𝑥↑2) + (𝑦↑2)))
41	39, 40	breqtrrd 4158	. . . . . . . . . . . . 13 ⊢ (((𝐴 ∈ ℕ0 ∧ 𝑥 ∈ (-𝐴...𝐴)) ∧ (𝑦 ∈ ℤ ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2)))) → (𝑦↑2) ≤ 𝐴)
42	23, 26, 22, 34, 41	letrd 8452	. . . . . . . . . . . 12 ⊢ (((𝐴 ∈ ℕ0 ∧ 𝑥 ∈ (-𝐴...𝐴)) ∧ (𝑦 ∈ ℤ ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2)))) → -𝑦 ≤ 𝐴)
43	21, 22, 42	lenegcon1d 8857	. . . . . . . . . . 11 ⊢ (((𝐴 ∈ ℕ0 ∧ 𝑥 ∈ (-𝐴...𝐴)) ∧ (𝑦 ∈ ℤ ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2)))) → -𝐴 ≤ 𝑦)
44		zzlesq 11161	. . . . . . . . . . . . 13 ⊢ (𝑦 ∈ ℤ → 𝑦 ≤ (𝑦↑2))
45	20, 44	syl 14	. . . . . . . . . . . 12 ⊢ (((𝐴 ∈ ℕ0 ∧ 𝑥 ∈ (-𝐴...𝐴)) ∧ (𝑦 ∈ ℤ ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2)))) → 𝑦 ≤ (𝑦↑2))
46	21, 26, 22, 45, 41	letrd 8452	. . . . . . . . . . 11 ⊢ (((𝐴 ∈ ℕ0 ∧ 𝑥 ∈ (-𝐴...𝐴)) ∧ (𝑦 ∈ ℤ ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2)))) → 𝑦 ≤ 𝐴)
47	18, 19, 20, 43, 46	elfzd 10430	. . . . . . . . . 10 ⊢ (((𝐴 ∈ ℕ0 ∧ 𝑥 ∈ (-𝐴...𝐴)) ∧ (𝑦 ∈ ℤ ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2)))) → 𝑦 ∈ (-𝐴...𝐴))
48	47, 40	jca 306	. . . . . . . . 9 ⊢ (((𝐴 ∈ ℕ0 ∧ 𝑥 ∈ (-𝐴...𝐴)) ∧ (𝑦 ∈ ℤ ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2)))) → (𝑦 ∈ (-𝐴...𝐴) ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2))))
49	48	ex 115	. . . . . . . 8 ⊢ ((𝐴 ∈ ℕ0 ∧ 𝑥 ∈ (-𝐴...𝐴)) → ((𝑦 ∈ ℤ ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2))) → (𝑦 ∈ (-𝐴...𝐴) ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2)))))
50	10	anim1i 340	. . . . . . . 8 ⊢ ((𝑦 ∈ (-𝐴...𝐴) ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2))) → (𝑦 ∈ ℤ ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2))))
51	49, 50	impbid1 142	. . . . . . 7 ⊢ ((𝐴 ∈ ℕ0 ∧ 𝑥 ∈ (-𝐴...𝐴)) → ((𝑦 ∈ ℤ ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2))) ↔ (𝑦 ∈ (-𝐴...𝐴) ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2)))))
52	51	rexbidv2 2553	. . . . . 6 ⊢ ((𝐴 ∈ ℕ0 ∧ 𝑥 ∈ (-𝐴...𝐴)) → (∃𝑦 ∈ ℤ 𝐴 = ((𝑥↑2) + (𝑦↑2)) ↔ ∃𝑦 ∈ (-𝐴...𝐴)𝐴 = ((𝑥↑2) + (𝑦↑2))))
53	52	dcbid 850	. . . . 5 ⊢ ((𝐴 ∈ ℕ0 ∧ 𝑥 ∈ (-𝐴...𝐴)) → (DECID ∃𝑦 ∈ ℤ 𝐴 = ((𝑥↑2) + (𝑦↑2)) ↔ DECID ∃𝑦 ∈ (-𝐴...𝐴)𝐴 = ((𝑥↑2) + (𝑦↑2))))
54	17, 53	mpbird 167	. . . 4 ⊢ ((𝐴 ∈ ℕ0 ∧ 𝑥 ∈ (-𝐴...𝐴)) → DECID ∃𝑦 ∈ ℤ 𝐴 = ((𝑥↑2) + (𝑦↑2)))
55	1, 2, 54	exfzdc 10670	. . 3 ⊢ (𝐴 ∈ ℕ0 → DECID ∃𝑥 ∈ (-𝐴...𝐴)∃𝑦 ∈ ℤ 𝐴 = ((𝑥↑2) + (𝑦↑2)))
56	1	ad3antrrr 496	. . . . . . . . . 10 ⊢ ((((𝐴 ∈ ℕ0 ∧ 𝑦 ∈ ℤ) ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2))) ∧ 𝑥 ∈ ℤ) → -𝐴 ∈ ℤ)
57	2	ad3antrrr 496	. . . . . . . . . 10 ⊢ ((((𝐴 ∈ ℕ0 ∧ 𝑦 ∈ ℤ) ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2))) ∧ 𝑥 ∈ ℤ) → 𝐴 ∈ ℤ)
58		simpr 110	. . . . . . . . . 10 ⊢ ((((𝐴 ∈ ℕ0 ∧ 𝑦 ∈ ℤ) ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2))) ∧ 𝑥 ∈ ℤ) → 𝑥 ∈ ℤ)
59	58	zred 9773	. . . . . . . . . . 11 ⊢ ((((𝐴 ∈ ℕ0 ∧ 𝑦 ∈ ℤ) ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2))) ∧ 𝑥 ∈ ℤ) → 𝑥 ∈ ℝ)
60	57	zred 9773	. . . . . . . . . . 11 ⊢ ((((𝐴 ∈ ℕ0 ∧ 𝑦 ∈ ℤ) ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2))) ∧ 𝑥 ∈ ℤ) → 𝐴 ∈ ℝ)
61	59	renegcld 8709	. . . . . . . . . . . 12 ⊢ ((((𝐴 ∈ ℕ0 ∧ 𝑦 ∈ ℤ) ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2))) ∧ 𝑥 ∈ ℤ) → -𝑥 ∈ ℝ)
62	59	resqcld 11152	. . . . . . . . . . . 12 ⊢ ((((𝐴 ∈ ℕ0 ∧ 𝑦 ∈ ℤ) ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2))) ∧ 𝑥 ∈ ℤ) → (𝑥↑2) ∈ ℝ)
63	58	znegcld 9775	. . . . . . . . . . . . . 14 ⊢ ((((𝐴 ∈ ℕ0 ∧ 𝑦 ∈ ℤ) ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2))) ∧ 𝑥 ∈ ℤ) → -𝑥 ∈ ℤ)
64		zzlesq 11161	. . . . . . . . . . . . . 14 ⊢ (-𝑥 ∈ ℤ → -𝑥 ≤ (-𝑥↑2))
65	63, 64	syl 14	. . . . . . . . . . . . 13 ⊢ ((((𝐴 ∈ ℕ0 ∧ 𝑦 ∈ ℤ) ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2))) ∧ 𝑥 ∈ ℤ) → -𝑥 ≤ (-𝑥↑2))
66	58	zcnd 9774	. . . . . . . . . . . . . 14 ⊢ ((((𝐴 ∈ ℕ0 ∧ 𝑦 ∈ ℤ) ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2))) ∧ 𝑥 ∈ ℤ) → 𝑥 ∈ ℂ)
67		sqneg 11050	. . . . . . . . . . . . . 14 ⊢ (𝑥 ∈ ℂ → (-𝑥↑2) = (𝑥↑2))
68	66, 67	syl 14	. . . . . . . . . . . . 13 ⊢ ((((𝐴 ∈ ℕ0 ∧ 𝑦 ∈ ℤ) ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2))) ∧ 𝑥 ∈ ℤ) → (-𝑥↑2) = (𝑥↑2))
69	65, 68	breqtrd 4156	. . . . . . . . . . . 12 ⊢ ((((𝐴 ∈ ℕ0 ∧ 𝑦 ∈ ℤ) ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2))) ∧ 𝑥 ∈ ℤ) → -𝑥 ≤ (𝑥↑2))
70	24	ad3antlr 497	. . . . . . . . . . . . . 14 ⊢ ((((𝐴 ∈ ℕ0 ∧ 𝑦 ∈ ℤ) ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2))) ∧ 𝑥 ∈ ℤ) → (𝑦↑2) ∈ ℕ0)
71		nn0addge1 9614	. . . . . . . . . . . . . 14 ⊢ (((𝑥↑2) ∈ ℝ ∧ (𝑦↑2) ∈ ℕ0) → (𝑥↑2) ≤ ((𝑥↑2) + (𝑦↑2)))
72	62, 70, 71	syl2anc 415	. . . . . . . . . . . . 13 ⊢ ((((𝐴 ∈ ℕ0 ∧ 𝑦 ∈ ℤ) ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2))) ∧ 𝑥 ∈ ℤ) → (𝑥↑2) ≤ ((𝑥↑2) + (𝑦↑2)))
73		simplr 533	. . . . . . . . . . . . 13 ⊢ ((((𝐴 ∈ ℕ0 ∧ 𝑦 ∈ ℤ) ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2))) ∧ 𝑥 ∈ ℤ) → 𝐴 = ((𝑥↑2) + (𝑦↑2)))
74	72, 73	breqtrrd 4158	. . . . . . . . . . . 12 ⊢ ((((𝐴 ∈ ℕ0 ∧ 𝑦 ∈ ℤ) ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2))) ∧ 𝑥 ∈ ℤ) → (𝑥↑2) ≤ 𝐴)
75	61, 62, 60, 69, 74	letrd 8452	. . . . . . . . . . 11 ⊢ ((((𝐴 ∈ ℕ0 ∧ 𝑦 ∈ ℤ) ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2))) ∧ 𝑥 ∈ ℤ) → -𝑥 ≤ 𝐴)
76	59, 60, 75	lenegcon1d 8857	. . . . . . . . . 10 ⊢ ((((𝐴 ∈ ℕ0 ∧ 𝑦 ∈ ℤ) ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2))) ∧ 𝑥 ∈ ℤ) → -𝐴 ≤ 𝑥)
77		zzlesq 11161	. . . . . . . . . . . 12 ⊢ (𝑥 ∈ ℤ → 𝑥 ≤ (𝑥↑2))
78	77	adantl 277	. . . . . . . . . . 11 ⊢ ((((𝐴 ∈ ℕ0 ∧ 𝑦 ∈ ℤ) ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2))) ∧ 𝑥 ∈ ℤ) → 𝑥 ≤ (𝑥↑2))
79	59, 62, 60, 78, 74	letrd 8452	. . . . . . . . . 10 ⊢ ((((𝐴 ∈ ℕ0 ∧ 𝑦 ∈ ℤ) ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2))) ∧ 𝑥 ∈ ℤ) → 𝑥 ≤ 𝐴)
80	56, 57, 58, 76, 79	elfzd 10430	. . . . . . . . 9 ⊢ ((((𝐴 ∈ ℕ0 ∧ 𝑦 ∈ ℤ) ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2))) ∧ 𝑥 ∈ ℤ) → 𝑥 ∈ (-𝐴...𝐴))
81	80	ex 115	. . . . . . . 8 ⊢ (((𝐴 ∈ ℕ0 ∧ 𝑦 ∈ ℤ) ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2))) → (𝑥 ∈ ℤ → 𝑥 ∈ (-𝐴...𝐴)))
82	81, 6	impbid1 142	. . . . . . 7 ⊢ (((𝐴 ∈ ℕ0 ∧ 𝑦 ∈ ℤ) ∧ 𝐴 = ((𝑥↑2) + (𝑦↑2))) → (𝑥 ∈ ℤ ↔ 𝑥 ∈ (-𝐴...𝐴)))
83	82	rexlimdva2 2671	. . . . . 6 ⊢ (𝐴 ∈ ℕ0 → (∃𝑦 ∈ ℤ 𝐴 = ((𝑥↑2) + (𝑦↑2)) → (𝑥 ∈ ℤ ↔ 𝑥 ∈ (-𝐴...𝐴))))
84	83	pm5.32rd 455	. . . . 5 ⊢ (𝐴 ∈ ℕ0 → ((𝑥 ∈ ℤ ∧ ∃𝑦 ∈ ℤ 𝐴 = ((𝑥↑2) + (𝑦↑2))) ↔ (𝑥 ∈ (-𝐴...𝐴) ∧ ∃𝑦 ∈ ℤ 𝐴 = ((𝑥↑2) + (𝑦↑2)))))
85	84	rexbidv2 2553	. . . 4 ⊢ (𝐴 ∈ ℕ0 → (∃𝑥 ∈ ℤ ∃𝑦 ∈ ℤ 𝐴 = ((𝑥↑2) + (𝑦↑2)) ↔ ∃𝑥 ∈ (-𝐴...𝐴)∃𝑦 ∈ ℤ 𝐴 = ((𝑥↑2) + (𝑦↑2))))
86	85	dcbid 850	. . 3 ⊢ (𝐴 ∈ ℕ0 → (DECID ∃𝑥 ∈ ℤ ∃𝑦 ∈ ℤ 𝐴 = ((𝑥↑2) + (𝑦↑2)) ↔ DECID ∃𝑥 ∈ (-𝐴...𝐴)∃𝑦 ∈ ℤ 𝐴 = ((𝑥↑2) + (𝑦↑2))))
87	55, 86	mpbird 167	. 2 ⊢ (𝐴 ∈ ℕ0 → DECID ∃𝑥 ∈ ℤ ∃𝑦 ∈ ℤ 𝐴 = ((𝑥↑2) + (𝑦↑2)))
88		eqeq1 2245	. . . . 5 ⊢ (𝑛 = 𝐴 → (𝑛 = ((𝑥↑2) + (𝑦↑2)) ↔ 𝐴 = ((𝑥↑2) + (𝑦↑2))))
89	88	2rexbidv 2575	. . . 4 ⊢ (𝑛 = 𝐴 → (∃𝑥 ∈ ℤ ∃𝑦 ∈ ℤ 𝑛 = ((𝑥↑2) + (𝑦↑2)) ↔ ∃𝑥 ∈ ℤ ∃𝑦 ∈ ℤ 𝐴 = ((𝑥↑2) + (𝑦↑2))))
90		4sqexercise2.s	. . . 4 ⊢ 𝑆 = {𝑛 ∣ ∃𝑥 ∈ ℤ ∃𝑦 ∈ ℤ 𝑛 = ((𝑥↑2) + (𝑦↑2))}
91	89, 90	elab2g 2973	. . 3 ⊢ (𝐴 ∈ ℕ0 → (𝐴 ∈ 𝑆 ↔ ∃𝑥 ∈ ℤ ∃𝑦 ∈ ℤ 𝐴 = ((𝑥↑2) + (𝑦↑2))))
92	91	dcbid 850	. 2 ⊢ (𝐴 ∈ ℕ0 → (DECID 𝐴 ∈ 𝑆 ↔ DECID ∃𝑥 ∈ ℤ ∃𝑦 ∈ ℤ 𝐴 = ((𝑥↑2) + (𝑦↑2))))
93	87, 92	mpbird 167	1 ⊢ (𝐴 ∈ ℕ0 → DECID 𝐴 ∈ 𝑆)

This proof depends on syntax axioms:   → wi 4   ∧ wa 104   ↔ wb 105  DECID wdc 846   = wceq 1402   ∈ wcel 2209  {cab 2224  ∃wrex 2529   class class class wbr 4130  (class class class)co 6085  ℂcc 8178  ℝcr 8179   + caddc 8183   ≤ cle 8362  -cneg 8500  2c2 9358  ℕ₀cn0 9568  ℤcz 9649  ...cfz 10422  ↑cexp 10990

This proof depends on axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 106  ax-ia2 107  ax-ia3 108  ax-in1 623  ax-in2 624  ax-io 721  ax-5 1500  ax-7 1501  ax-gen 1502  ax-ie1 1546  ax-ie2 1547  ax-8 1557  ax-10 1558  ax-11 1559  ax-i12 1560  ax-bndl 1562  ax-4 1563  ax-17 1579  ax-i9 1583  ax-ial 1587  ax-i5r 1588  ax-14 2212  ax-ext 2220  ax-coll 4246  ax-sep 4249  ax-nul 4259  ax-pow 4311  ax-pr 4346  ax-un 4578  ax-setind 4684  ax-iinf 4735  ax-cnex 8271  ax-resscn 8272  ax-1cn 8273  ax-1re 8274  ax-icn 8275  ax-addcl 8276  ax-addrcl 8277  ax-mulcl 8278  ax-mulrcl 8279  ax-addcom 8280  ax-mulcom 8281  ax-addass 8282  ax-mulass 8283  ax-distr 8284  ax-i2m1 8285  ax-0lt1 8286  ax-1rid 8287  ax-0id 8288  ax-rnegex 8289  ax-precex 8290  ax-cnre 8291  ax-pre-ltirr 8292  ax-pre-ltwlin 8293  ax-pre-lttrn 8294  ax-pre-apti 8295  ax-pre-ltadd 8296  ax-pre-mulgt0 8297  ax-pre-mulext 8298

This proof depends on definitions:  df-bi 117  df-dc 847  df-3or 1010  df-3an 1011  df-tru 1405  df-fal 1408  df-nf 1514  df-sb 1816  df-eu 2089  df-mo 2090  df-clab 2225  df-cleq 2231  df-clel 2234  df-nfc 2381  df-ne 2421  df-nel 2516  df-ral 2533  df-rex 2534  df-reu 2535  df-rmo 2536  df-rab 2537  df-v 2823  df-sbc 3052  df-csb 3148  df-dif 3222  df-un 3224  df-in 3226  df-ss 3233  df-nul 3521  df-if 3639  df-pw 3690  df-sn 3715  df-pr 3716  df-op 3718  df-uni 3936  df-int 3971  df-iun 4014  df-br 4131  df-opab 4193  df-mpt 4194  df-tr 4230  df-id 4438  df-po 4441  df-iso 4442  df-iord 4511  df-on 4513  df-ilim 4514  df-suc 4516  df-iom 4738  df-xp 4780  df-rel 4781  df-cnv 4782  df-co 4783  df-dm 4784  df-rn 4785  df-res 4786  df-ima 4787  df-iota 5337  df-fun 5379  df-fn 5380  df-f 5381  df-f1 5382  df-fo 5383  df-f1o 5384  df-fv 5385  df-riota 6038  df-ov 6088  df-oprab 6089  df-mpo 6090  df-1st 6374  df-2nd 6375  df-recs 6576  df-frec 6662  df-pnf 8363  df-mnf 8364  df-xr 8365  df-ltxr 8366  df-le 8367  df-sub 8501  df-neg 8502  df-reap 8906  df-ap 8913  df-div 9006  df-inn 9308  df-2 9366  df-n0 9569  df-z 9650  df-uz 9932  df-fz 10423  df-fzo 10561  df-seqfrec 10900  df-exp 10991

This theorem is used by: (None)