4sqlem1 - Metamath Proof Explorer

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Theorem 4sqlem1 16919

Description: Lemma for 4sq 16935. The set 𝑆 is the set of all numbers that are expressible as a sum of four squares. Our goal is to show that 𝑆 = ℕ₀; here we show one subset direction. (Contributed by Mario Carneiro, 14-Jul-2014.)

**Hypothesis**
Ref	Expression
4sq.1	⊢ 𝑆 = {𝑛 ∣ ∃𝑥 ∈ ℤ ∃𝑦 ∈ ℤ ∃𝑧 ∈ ℤ ∃𝑤 ∈ ℤ 𝑛 = (((𝑥↑2) + (𝑦↑2)) + ((𝑧↑2) + (𝑤↑2)))}

**Assertion**
Ref	Expression
4sqlem1	⊢ 𝑆 ⊆ ℕ₀

Distinct variable groups: 𝑤,𝑛,𝑥,𝑦,𝑧 𝑆,𝑛 Allowed substitution hints: 𝑆(𝑥,𝑦,𝑧,𝑤)

**Proof of Theorem 4sqlem1**
Step	Hyp	Ref	Expression
1		4sq.1	. 2 ⊢ 𝑆 = {𝑛 ∣ ∃𝑥 ∈ ℤ ∃𝑦 ∈ ℤ ∃𝑧 ∈ ℤ ∃𝑤 ∈ ℤ 𝑛 = (((𝑥↑2) + (𝑦↑2)) + ((𝑧↑2) + (𝑤↑2)))}
2		zsqcl2 14103	. . . . . . . 8 ⊢ (𝑥 ∈ ℤ → (𝑥↑2) ∈ ℕ₀)
3		zsqcl2 14103	. . . . . . . 8 ⊢ (𝑦 ∈ ℤ → (𝑦↑2) ∈ ℕ₀)
4		nn0addcl 12477	. . . . . . . 8 ⊢ (((𝑥↑2) ∈ ℕ₀ ∧ (𝑦↑2) ∈ ℕ₀) → ((𝑥↑2) + (𝑦↑2)) ∈ ℕ₀)
5	2, 3, 4	syl2an 596	. . . . . . 7 ⊢ ((𝑥 ∈ ℤ ∧ 𝑦 ∈ ℤ) → ((𝑥↑2) + (𝑦↑2)) ∈ ℕ₀)
6		zsqcl2 14103	. . . . . . . 8 ⊢ (𝑧 ∈ ℤ → (𝑧↑2) ∈ ℕ₀)
7		zsqcl2 14103	. . . . . . . 8 ⊢ (𝑤 ∈ ℤ → (𝑤↑2) ∈ ℕ₀)
8		nn0addcl 12477	. . . . . . . 8 ⊢ (((𝑧↑2) ∈ ℕ₀ ∧ (𝑤↑2) ∈ ℕ₀) → ((𝑧↑2) + (𝑤↑2)) ∈ ℕ₀)
9	6, 7, 8	syl2an 596	. . . . . . 7 ⊢ ((𝑧 ∈ ℤ ∧ 𝑤 ∈ ℤ) → ((𝑧↑2) + (𝑤↑2)) ∈ ℕ₀)
10		nn0addcl 12477	. . . . . . 7 ⊢ ((((𝑥↑2) + (𝑦↑2)) ∈ ℕ₀ ∧ ((𝑧↑2) + (𝑤↑2)) ∈ ℕ₀) → (((𝑥↑2) + (𝑦↑2)) + ((𝑧↑2) + (𝑤↑2))) ∈ ℕ₀)
11	5, 9, 10	syl2an 596	. . . . . 6 ⊢ (((𝑥 ∈ ℤ ∧ 𝑦 ∈ ℤ) ∧ (𝑧 ∈ ℤ ∧ 𝑤 ∈ ℤ)) → (((𝑥↑2) + (𝑦↑2)) + ((𝑧↑2) + (𝑤↑2))) ∈ ℕ₀)
12		eleq1a 2823	. . . . . 6 ⊢ ((((𝑥↑2) + (𝑦↑2)) + ((𝑧↑2) + (𝑤↑2))) ∈ ℕ₀ → (𝑛 = (((𝑥↑2) + (𝑦↑2)) + ((𝑧↑2) + (𝑤↑2))) → 𝑛 ∈ ℕ₀))
13	11, 12	syl 17	. . . . 5 ⊢ (((𝑥 ∈ ℤ ∧ 𝑦 ∈ ℤ) ∧ (𝑧 ∈ ℤ ∧ 𝑤 ∈ ℤ)) → (𝑛 = (((𝑥↑2) + (𝑦↑2)) + ((𝑧↑2) + (𝑤↑2))) → 𝑛 ∈ ℕ₀))
14	13	rexlimdvva 3194	. . . 4 ⊢ ((𝑥 ∈ ℤ ∧ 𝑦 ∈ ℤ) → (∃𝑧 ∈ ℤ ∃𝑤 ∈ ℤ 𝑛 = (((𝑥↑2) + (𝑦↑2)) + ((𝑧↑2) + (𝑤↑2))) → 𝑛 ∈ ℕ₀))
15	14	rexlimivv 3179	. . 3 ⊢ (∃𝑥 ∈ ℤ ∃𝑦 ∈ ℤ ∃𝑧 ∈ ℤ ∃𝑤 ∈ ℤ 𝑛 = (((𝑥↑2) + (𝑦↑2)) + ((𝑧↑2) + (𝑤↑2))) → 𝑛 ∈ ℕ₀)
16	15	abssi 4033	. 2 ⊢ {𝑛 ∣ ∃𝑥 ∈ ℤ ∃𝑦 ∈ ℤ ∃𝑧 ∈ ℤ ∃𝑤 ∈ ℤ 𝑛 = (((𝑥↑2) + (𝑦↑2)) + ((𝑧↑2) + (𝑤↑2)))} ⊆ ℕ₀
17	1, 16	eqsstri 3993	1 ⊢ 𝑆 ⊆ ℕ₀

Colors of variables: wff setvar class

Syntax hints: → wi 4 ∧ wa 395 = wceq 1540 ∈ wcel 2109 {cab 2707 ∃wrex 3053 ⊆ wss 3914 (class class class)co 7387 + caddc 11071 2c2 12241 ℕ₀cn0 12442 ℤcz 12529 ↑cexp 14026

This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1795 ax-4 1809 ax-5 1910 ax-6 1967 ax-7 2008 ax-8 2111 ax-9 2119 ax-10 2142 ax-11 2158 ax-12 2178 ax-ext 2701 ax-sep 5251 ax-nul 5261 ax-pow 5320 ax-pr 5387 ax-un 7711 ax-cnex 11124 ax-resscn 11125 ax-1cn 11126 ax-icn 11127 ax-addcl 11128 ax-addrcl 11129 ax-mulcl 11130 ax-mulrcl 11131 ax-mulcom 11132 ax-addass 11133 ax-mulass 11134 ax-distr 11135 ax-i2m1 11136 ax-1ne0 11137 ax-1rid 11138 ax-rnegex 11139 ax-rrecex 11140 ax-cnre 11141 ax-pre-lttri 11142 ax-pre-lttrn 11143 ax-pre-ltadd 11144 ax-pre-mulgt0 11145

This theorem depends on definitions: df-bi 207 df-an 396 df-or 848 df-3or 1087 df-3an 1088 df-tru 1543 df-fal 1553 df-ex 1780 df-nf 1784 df-sb 2066 df-mo 2533 df-eu 2562 df-clab 2708 df-cleq 2721 df-clel 2803 df-nfc 2878 df-ne 2926 df-nel 3030 df-ral 3045 df-rex 3054 df-reu 3355 df-rab 3406 df-v 3449 df-sbc 3754 df-csb 3863 df-dif 3917 df-un 3919 df-in 3921 df-ss 3931 df-pss 3934 df-nul 4297 df-if 4489 df-pw 4565 df-sn 4590 df-pr 4592 df-op 4596 df-uni 4872 df-iun 4957 df-br 5108 df-opab 5170 df-mpt 5189 df-tr 5215 df-id 5533 df-eprel 5538 df-po 5546 df-so 5547 df-fr 5591 df-we 5593 df-xp 5644 df-rel 5645 df-cnv 5646 df-co 5647 df-dm 5648 df-rn 5649 df-res 5650 df-ima 5651 df-pred 6274 df-ord 6335 df-on 6336 df-lim 6337 df-suc 6338 df-iota 6464 df-fun 6513 df-fn 6514 df-f 6515 df-f1 6516 df-fo 6517 df-f1o 6518 df-fv 6519 df-riota 7344 df-ov 7390 df-oprab 7391 df-mpo 7392 df-om 7843 df-2nd 7969 df-frecs 8260 df-wrecs 8291 df-recs 8340 df-rdg 8378 df-er 8671 df-en 8919 df-dom 8920 df-sdom 8921 df-pnf 11210 df-mnf 11211 df-xr 11212 df-ltxr 11213 df-le 11214 df-sub 11407 df-neg 11408 df-nn 12187 df-2 12249 df-n0 12443 df-z 12530 df-uz 12794 df-seq 13967 df-exp 14027

This theorem is referenced by: 4sqlem19 16934

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