Users' Mathboxes Mathbox for Norm Megill < Previous   Next >
Nearby theorems
Mirrors  >  Home  >  MPE Home  >  Th. List  >   Mathboxes  >  cdleme22d Structured version   Visualization version   GIF version

Theorem cdleme22d 37584
Description: Part of proof of Lemma E in [Crawley] p. 113, 3rd paragraph, 9th line on p. 115. (Contributed by NM, 4-Dec-2012.)
Hypotheses
Ref Expression
cdleme22.l = (le‘𝐾)
cdleme22.j = (join‘𝐾)
cdleme22.m = (meet‘𝐾)
cdleme22.a 𝐴 = (Atoms‘𝐾)
cdleme22.h 𝐻 = (LHyp‘𝐾)
Assertion
Ref Expression
cdleme22d (((𝐾 ∈ HL ∧ 𝑊𝐻) ∧ ((𝑆𝐴 ∧ ¬ 𝑆 𝑊) ∧ (𝑇𝐴 ∧ ¬ 𝑇 𝑊) ∧ (𝑉𝐴𝑉 𝑊)) ∧ (𝑆𝑇𝑆 (𝑇 𝑉))) → 𝑉 = ((𝑆 𝑇) 𝑊))

Proof of Theorem cdleme22d
StepHypRef Expression
1 simp3r 1199 . . . . . 6 (((𝐾 ∈ HL ∧ 𝑊𝐻) ∧ ((𝑆𝐴 ∧ ¬ 𝑆 𝑊) ∧ (𝑇𝐴 ∧ ¬ 𝑇 𝑊) ∧ (𝑉𝐴𝑉 𝑊)) ∧ (𝑆𝑇𝑆 (𝑇 𝑉))) → 𝑆 (𝑇 𝑉))
2 simp1l 1194 . . . . . . 7 (((𝐾 ∈ HL ∧ 𝑊𝐻) ∧ ((𝑆𝐴 ∧ ¬ 𝑆 𝑊) ∧ (𝑇𝐴 ∧ ¬ 𝑇 𝑊) ∧ (𝑉𝐴𝑉 𝑊)) ∧ (𝑆𝑇𝑆 (𝑇 𝑉))) → 𝐾 ∈ HL)
3 simp22l 1289 . . . . . . 7 (((𝐾 ∈ HL ∧ 𝑊𝐻) ∧ ((𝑆𝐴 ∧ ¬ 𝑆 𝑊) ∧ (𝑇𝐴 ∧ ¬ 𝑇 𝑊) ∧ (𝑉𝐴𝑉 𝑊)) ∧ (𝑆𝑇𝑆 (𝑇 𝑉))) → 𝑇𝐴)
4 simp23l 1291 . . . . . . 7 (((𝐾 ∈ HL ∧ 𝑊𝐻) ∧ ((𝑆𝐴 ∧ ¬ 𝑆 𝑊) ∧ (𝑇𝐴 ∧ ¬ 𝑇 𝑊) ∧ (𝑉𝐴𝑉 𝑊)) ∧ (𝑆𝑇𝑆 (𝑇 𝑉))) → 𝑉𝐴)
5 cdleme22.l . . . . . . . 8 = (le‘𝐾)
6 cdleme22.j . . . . . . . 8 = (join‘𝐾)
7 cdleme22.a . . . . . . . 8 𝐴 = (Atoms‘𝐾)
85, 6, 7hlatlej1 36616 . . . . . . 7 ((𝐾 ∈ HL ∧ 𝑇𝐴𝑉𝐴) → 𝑇 (𝑇 𝑉))
92, 3, 4, 8syl3anc 1368 . . . . . 6 (((𝐾 ∈ HL ∧ 𝑊𝐻) ∧ ((𝑆𝐴 ∧ ¬ 𝑆 𝑊) ∧ (𝑇𝐴 ∧ ¬ 𝑇 𝑊) ∧ (𝑉𝐴𝑉 𝑊)) ∧ (𝑆𝑇𝑆 (𝑇 𝑉))) → 𝑇 (𝑇 𝑉))
102hllatd 36605 . . . . . . 7 (((𝐾 ∈ HL ∧ 𝑊𝐻) ∧ ((𝑆𝐴 ∧ ¬ 𝑆 𝑊) ∧ (𝑇𝐴 ∧ ¬ 𝑇 𝑊) ∧ (𝑉𝐴𝑉 𝑊)) ∧ (𝑆𝑇𝑆 (𝑇 𝑉))) → 𝐾 ∈ Lat)
11 simp21l 1287 . . . . . . . 8 (((𝐾 ∈ HL ∧ 𝑊𝐻) ∧ ((𝑆𝐴 ∧ ¬ 𝑆 𝑊) ∧ (𝑇𝐴 ∧ ¬ 𝑇 𝑊) ∧ (𝑉𝐴𝑉 𝑊)) ∧ (𝑆𝑇𝑆 (𝑇 𝑉))) → 𝑆𝐴)
12 eqid 2824 . . . . . . . . 9 (Base‘𝐾) = (Base‘𝐾)
1312, 7atbase 36530 . . . . . . . 8 (𝑆𝐴𝑆 ∈ (Base‘𝐾))
1411, 13syl 17 . . . . . . 7 (((𝐾 ∈ HL ∧ 𝑊𝐻) ∧ ((𝑆𝐴 ∧ ¬ 𝑆 𝑊) ∧ (𝑇𝐴 ∧ ¬ 𝑇 𝑊) ∧ (𝑉𝐴𝑉 𝑊)) ∧ (𝑆𝑇𝑆 (𝑇 𝑉))) → 𝑆 ∈ (Base‘𝐾))
1512, 7atbase 36530 . . . . . . . 8 (𝑇𝐴𝑇 ∈ (Base‘𝐾))
163, 15syl 17 . . . . . . 7 (((𝐾 ∈ HL ∧ 𝑊𝐻) ∧ ((𝑆𝐴 ∧ ¬ 𝑆 𝑊) ∧ (𝑇𝐴 ∧ ¬ 𝑇 𝑊) ∧ (𝑉𝐴𝑉 𝑊)) ∧ (𝑆𝑇𝑆 (𝑇 𝑉))) → 𝑇 ∈ (Base‘𝐾))
1712, 6, 7hlatjcl 36608 . . . . . . . 8 ((𝐾 ∈ HL ∧ 𝑇𝐴𝑉𝐴) → (𝑇 𝑉) ∈ (Base‘𝐾))
182, 3, 4, 17syl3anc 1368 . . . . . . 7 (((𝐾 ∈ HL ∧ 𝑊𝐻) ∧ ((𝑆𝐴 ∧ ¬ 𝑆 𝑊) ∧ (𝑇𝐴 ∧ ¬ 𝑇 𝑊) ∧ (𝑉𝐴𝑉 𝑊)) ∧ (𝑆𝑇𝑆 (𝑇 𝑉))) → (𝑇 𝑉) ∈ (Base‘𝐾))
1912, 5, 6latjle12 17672 . . . . . . 7 ((𝐾 ∈ Lat ∧ (𝑆 ∈ (Base‘𝐾) ∧ 𝑇 ∈ (Base‘𝐾) ∧ (𝑇 𝑉) ∈ (Base‘𝐾))) → ((𝑆 (𝑇 𝑉) ∧ 𝑇 (𝑇 𝑉)) ↔ (𝑆 𝑇) (𝑇 𝑉)))
2010, 14, 16, 18, 19syl13anc 1369 . . . . . 6 (((𝐾 ∈ HL ∧ 𝑊𝐻) ∧ ((𝑆𝐴 ∧ ¬ 𝑆 𝑊) ∧ (𝑇𝐴 ∧ ¬ 𝑇 𝑊) ∧ (𝑉𝐴𝑉 𝑊)) ∧ (𝑆𝑇𝑆 (𝑇 𝑉))) → ((𝑆 (𝑇 𝑉) ∧ 𝑇 (𝑇 𝑉)) ↔ (𝑆 𝑇) (𝑇 𝑉)))
211, 9, 20mpbi2and 711 . . . . 5 (((𝐾 ∈ HL ∧ 𝑊𝐻) ∧ ((𝑆𝐴 ∧ ¬ 𝑆 𝑊) ∧ (𝑇𝐴 ∧ ¬ 𝑇 𝑊) ∧ (𝑉𝐴𝑉 𝑊)) ∧ (𝑆𝑇𝑆 (𝑇 𝑉))) → (𝑆 𝑇) (𝑇 𝑉))
2212, 6, 7hlatjcl 36608 . . . . . . 7 ((𝐾 ∈ HL ∧ 𝑆𝐴𝑇𝐴) → (𝑆 𝑇) ∈ (Base‘𝐾))
232, 11, 3, 22syl3anc 1368 . . . . . 6 (((𝐾 ∈ HL ∧ 𝑊𝐻) ∧ ((𝑆𝐴 ∧ ¬ 𝑆 𝑊) ∧ (𝑇𝐴 ∧ ¬ 𝑇 𝑊) ∧ (𝑉𝐴𝑉 𝑊)) ∧ (𝑆𝑇𝑆 (𝑇 𝑉))) → (𝑆 𝑇) ∈ (Base‘𝐾))
24 simp1r 1195 . . . . . . 7 (((𝐾 ∈ HL ∧ 𝑊𝐻) ∧ ((𝑆𝐴 ∧ ¬ 𝑆 𝑊) ∧ (𝑇𝐴 ∧ ¬ 𝑇 𝑊) ∧ (𝑉𝐴𝑉 𝑊)) ∧ (𝑆𝑇𝑆 (𝑇 𝑉))) → 𝑊𝐻)
25 cdleme22.h . . . . . . . 8 𝐻 = (LHyp‘𝐾)
2612, 25lhpbase 37239 . . . . . . 7 (𝑊𝐻𝑊 ∈ (Base‘𝐾))
2724, 26syl 17 . . . . . 6 (((𝐾 ∈ HL ∧ 𝑊𝐻) ∧ ((𝑆𝐴 ∧ ¬ 𝑆 𝑊) ∧ (𝑇𝐴 ∧ ¬ 𝑇 𝑊) ∧ (𝑉𝐴𝑉 𝑊)) ∧ (𝑆𝑇𝑆 (𝑇 𝑉))) → 𝑊 ∈ (Base‘𝐾))
28 cdleme22.m . . . . . . 7 = (meet‘𝐾)
2912, 5, 28latmlem1 17691 . . . . . 6 ((𝐾 ∈ Lat ∧ ((𝑆 𝑇) ∈ (Base‘𝐾) ∧ (𝑇 𝑉) ∈ (Base‘𝐾) ∧ 𝑊 ∈ (Base‘𝐾))) → ((𝑆 𝑇) (𝑇 𝑉) → ((𝑆 𝑇) 𝑊) ((𝑇 𝑉) 𝑊)))
3010, 23, 18, 27, 29syl13anc 1369 . . . . 5 (((𝐾 ∈ HL ∧ 𝑊𝐻) ∧ ((𝑆𝐴 ∧ ¬ 𝑆 𝑊) ∧ (𝑇𝐴 ∧ ¬ 𝑇 𝑊) ∧ (𝑉𝐴𝑉 𝑊)) ∧ (𝑆𝑇𝑆 (𝑇 𝑉))) → ((𝑆 𝑇) (𝑇 𝑉) → ((𝑆 𝑇) 𝑊) ((𝑇 𝑉) 𝑊)))
3121, 30mpd 15 . . . 4 (((𝐾 ∈ HL ∧ 𝑊𝐻) ∧ ((𝑆𝐴 ∧ ¬ 𝑆 𝑊) ∧ (𝑇𝐴 ∧ ¬ 𝑇 𝑊) ∧ (𝑉𝐴𝑉 𝑊)) ∧ (𝑆𝑇𝑆 (𝑇 𝑉))) → ((𝑆 𝑇) 𝑊) ((𝑇 𝑉) 𝑊))
32 simp1 1133 . . . . . . 7 (((𝐾 ∈ HL ∧ 𝑊𝐻) ∧ ((𝑆𝐴 ∧ ¬ 𝑆 𝑊) ∧ (𝑇𝐴 ∧ ¬ 𝑇 𝑊) ∧ (𝑉𝐴𝑉 𝑊)) ∧ (𝑆𝑇𝑆 (𝑇 𝑉))) → (𝐾 ∈ HL ∧ 𝑊𝐻))
33 simp22 1204 . . . . . . 7 (((𝐾 ∈ HL ∧ 𝑊𝐻) ∧ ((𝑆𝐴 ∧ ¬ 𝑆 𝑊) ∧ (𝑇𝐴 ∧ ¬ 𝑇 𝑊) ∧ (𝑉𝐴𝑉 𝑊)) ∧ (𝑆𝑇𝑆 (𝑇 𝑉))) → (𝑇𝐴 ∧ ¬ 𝑇 𝑊))
34 eqid 2824 . . . . . . . 8 (0.‘𝐾) = (0.‘𝐾)
355, 28, 34, 7, 25lhpmat 37271 . . . . . . 7 (((𝐾 ∈ HL ∧ 𝑊𝐻) ∧ (𝑇𝐴 ∧ ¬ 𝑇 𝑊)) → (𝑇 𝑊) = (0.‘𝐾))
3632, 33, 35syl2anc 587 . . . . . 6 (((𝐾 ∈ HL ∧ 𝑊𝐻) ∧ ((𝑆𝐴 ∧ ¬ 𝑆 𝑊) ∧ (𝑇𝐴 ∧ ¬ 𝑇 𝑊) ∧ (𝑉𝐴𝑉 𝑊)) ∧ (𝑆𝑇𝑆 (𝑇 𝑉))) → (𝑇 𝑊) = (0.‘𝐾))
3736oveq1d 7164 . . . . 5 (((𝐾 ∈ HL ∧ 𝑊𝐻) ∧ ((𝑆𝐴 ∧ ¬ 𝑆 𝑊) ∧ (𝑇𝐴 ∧ ¬ 𝑇 𝑊) ∧ (𝑉𝐴𝑉 𝑊)) ∧ (𝑆𝑇𝑆 (𝑇 𝑉))) → ((𝑇 𝑊) 𝑉) = ((0.‘𝐾) 𝑉))
38 simp23r 1292 . . . . . 6 (((𝐾 ∈ HL ∧ 𝑊𝐻) ∧ ((𝑆𝐴 ∧ ¬ 𝑆 𝑊) ∧ (𝑇𝐴 ∧ ¬ 𝑇 𝑊) ∧ (𝑉𝐴𝑉 𝑊)) ∧ (𝑆𝑇𝑆 (𝑇 𝑉))) → 𝑉 𝑊)
3912, 5, 6, 28, 7atmod4i1 37107 . . . . . 6 ((𝐾 ∈ HL ∧ (𝑉𝐴𝑇 ∈ (Base‘𝐾) ∧ 𝑊 ∈ (Base‘𝐾)) ∧ 𝑉 𝑊) → ((𝑇 𝑊) 𝑉) = ((𝑇 𝑉) 𝑊))
402, 4, 16, 27, 38, 39syl131anc 1380 . . . . 5 (((𝐾 ∈ HL ∧ 𝑊𝐻) ∧ ((𝑆𝐴 ∧ ¬ 𝑆 𝑊) ∧ (𝑇𝐴 ∧ ¬ 𝑇 𝑊) ∧ (𝑉𝐴𝑉 𝑊)) ∧ (𝑆𝑇𝑆 (𝑇 𝑉))) → ((𝑇 𝑊) 𝑉) = ((𝑇 𝑉) 𝑊))
41 hlol 36602 . . . . . . 7 (𝐾 ∈ HL → 𝐾 ∈ OL)
422, 41syl 17 . . . . . 6 (((𝐾 ∈ HL ∧ 𝑊𝐻) ∧ ((𝑆𝐴 ∧ ¬ 𝑆 𝑊) ∧ (𝑇𝐴 ∧ ¬ 𝑇 𝑊) ∧ (𝑉𝐴𝑉 𝑊)) ∧ (𝑆𝑇𝑆 (𝑇 𝑉))) → 𝐾 ∈ OL)
4312, 7atbase 36530 . . . . . . 7 (𝑉𝐴𝑉 ∈ (Base‘𝐾))
444, 43syl 17 . . . . . 6 (((𝐾 ∈ HL ∧ 𝑊𝐻) ∧ ((𝑆𝐴 ∧ ¬ 𝑆 𝑊) ∧ (𝑇𝐴 ∧ ¬ 𝑇 𝑊) ∧ (𝑉𝐴𝑉 𝑊)) ∧ (𝑆𝑇𝑆 (𝑇 𝑉))) → 𝑉 ∈ (Base‘𝐾))
4512, 6, 34olj02 36467 . . . . . 6 ((𝐾 ∈ OL ∧ 𝑉 ∈ (Base‘𝐾)) → ((0.‘𝐾) 𝑉) = 𝑉)
4642, 44, 45syl2anc 587 . . . . 5 (((𝐾 ∈ HL ∧ 𝑊𝐻) ∧ ((𝑆𝐴 ∧ ¬ 𝑆 𝑊) ∧ (𝑇𝐴 ∧ ¬ 𝑇 𝑊) ∧ (𝑉𝐴𝑉 𝑊)) ∧ (𝑆𝑇𝑆 (𝑇 𝑉))) → ((0.‘𝐾) 𝑉) = 𝑉)
4737, 40, 463eqtr3d 2867 . . . 4 (((𝐾 ∈ HL ∧ 𝑊𝐻) ∧ ((𝑆𝐴 ∧ ¬ 𝑆 𝑊) ∧ (𝑇𝐴 ∧ ¬ 𝑇 𝑊) ∧ (𝑉𝐴𝑉 𝑊)) ∧ (𝑆𝑇𝑆 (𝑇 𝑉))) → ((𝑇 𝑉) 𝑊) = 𝑉)
4831, 47breqtrd 5078 . . 3 (((𝐾 ∈ HL ∧ 𝑊𝐻) ∧ ((𝑆𝐴 ∧ ¬ 𝑆 𝑊) ∧ (𝑇𝐴 ∧ ¬ 𝑇 𝑊) ∧ (𝑉𝐴𝑉 𝑊)) ∧ (𝑆𝑇𝑆 (𝑇 𝑉))) → ((𝑆 𝑇) 𝑊) 𝑉)
49 hlatl 36601 . . . . 5 (𝐾 ∈ HL → 𝐾 ∈ AtLat)
502, 49syl 17 . . . 4 (((𝐾 ∈ HL ∧ 𝑊𝐻) ∧ ((𝑆𝐴 ∧ ¬ 𝑆 𝑊) ∧ (𝑇𝐴 ∧ ¬ 𝑇 𝑊) ∧ (𝑉𝐴𝑉 𝑊)) ∧ (𝑆𝑇𝑆 (𝑇 𝑉))) → 𝐾 ∈ AtLat)
51 simp21r 1288 . . . . 5 (((𝐾 ∈ HL ∧ 𝑊𝐻) ∧ ((𝑆𝐴 ∧ ¬ 𝑆 𝑊) ∧ (𝑇𝐴 ∧ ¬ 𝑇 𝑊) ∧ (𝑉𝐴𝑉 𝑊)) ∧ (𝑆𝑇𝑆 (𝑇 𝑉))) → ¬ 𝑆 𝑊)
52 simp3l 1198 . . . . 5 (((𝐾 ∈ HL ∧ 𝑊𝐻) ∧ ((𝑆𝐴 ∧ ¬ 𝑆 𝑊) ∧ (𝑇𝐴 ∧ ¬ 𝑇 𝑊) ∧ (𝑉𝐴𝑉 𝑊)) ∧ (𝑆𝑇𝑆 (𝑇 𝑉))) → 𝑆𝑇)
535, 6, 28, 7, 25lhpat 37284 . . . . 5 (((𝐾 ∈ HL ∧ 𝑊𝐻) ∧ (𝑆𝐴 ∧ ¬ 𝑆 𝑊) ∧ (𝑇𝐴𝑆𝑇)) → ((𝑆 𝑇) 𝑊) ∈ 𝐴)
542, 24, 11, 51, 3, 52, 53syl222anc 1383 . . . 4 (((𝐾 ∈ HL ∧ 𝑊𝐻) ∧ ((𝑆𝐴 ∧ ¬ 𝑆 𝑊) ∧ (𝑇𝐴 ∧ ¬ 𝑇 𝑊) ∧ (𝑉𝐴𝑉 𝑊)) ∧ (𝑆𝑇𝑆 (𝑇 𝑉))) → ((𝑆 𝑇) 𝑊) ∈ 𝐴)
555, 7atcmp 36552 . . . 4 ((𝐾 ∈ AtLat ∧ ((𝑆 𝑇) 𝑊) ∈ 𝐴𝑉𝐴) → (((𝑆 𝑇) 𝑊) 𝑉 ↔ ((𝑆 𝑇) 𝑊) = 𝑉))
5650, 54, 4, 55syl3anc 1368 . . 3 (((𝐾 ∈ HL ∧ 𝑊𝐻) ∧ ((𝑆𝐴 ∧ ¬ 𝑆 𝑊) ∧ (𝑇𝐴 ∧ ¬ 𝑇 𝑊) ∧ (𝑉𝐴𝑉 𝑊)) ∧ (𝑆𝑇𝑆 (𝑇 𝑉))) → (((𝑆 𝑇) 𝑊) 𝑉 ↔ ((𝑆 𝑇) 𝑊) = 𝑉))
5748, 56mpbid 235 . 2 (((𝐾 ∈ HL ∧ 𝑊𝐻) ∧ ((𝑆𝐴 ∧ ¬ 𝑆 𝑊) ∧ (𝑇𝐴 ∧ ¬ 𝑇 𝑊) ∧ (𝑉𝐴𝑉 𝑊)) ∧ (𝑆𝑇𝑆 (𝑇 𝑉))) → ((𝑆 𝑇) 𝑊) = 𝑉)
5857eqcomd 2830 1 (((𝐾 ∈ HL ∧ 𝑊𝐻) ∧ ((𝑆𝐴 ∧ ¬ 𝑆 𝑊) ∧ (𝑇𝐴 ∧ ¬ 𝑇 𝑊) ∧ (𝑉𝐴𝑉 𝑊)) ∧ (𝑆𝑇𝑆 (𝑇 𝑉))) → 𝑉 = ((𝑆 𝑇) 𝑊))
Colors of variables: wff setvar class
Syntax hints:  ¬ wn 3  wi 4  wb 209  wa 399  w3a 1084   = wceq 1538  wcel 2115  wne 3014   class class class wbr 5052  cfv 6343  (class class class)co 7149  Basecbs 16483  lecple 16572  joincjn 17554  meetcmee 17555  0.cp0 17647  Latclat 17655  OLcol 36415  Atomscatm 36504  AtLatcal 36505  HLchlt 36591  LHypclh 37225
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1797  ax-4 1811  ax-5 1912  ax-6 1971  ax-7 2016  ax-8 2117  ax-9 2125  ax-10 2146  ax-11 2162  ax-12 2179  ax-ext 2796  ax-rep 5176  ax-sep 5189  ax-nul 5196  ax-pow 5253  ax-pr 5317  ax-un 7455
This theorem depends on definitions:  df-bi 210  df-an 400  df-or 845  df-3an 1086  df-tru 1541  df-ex 1782  df-nf 1786  df-sb 2071  df-mo 2624  df-eu 2655  df-clab 2803  df-cleq 2817  df-clel 2896  df-nfc 2964  df-ne 3015  df-ral 3138  df-rex 3139  df-reu 3140  df-rab 3142  df-v 3482  df-sbc 3759  df-csb 3867  df-dif 3922  df-un 3924  df-in 3926  df-ss 3936  df-nul 4277  df-if 4451  df-pw 4524  df-sn 4551  df-pr 4553  df-op 4557  df-uni 4825  df-iun 4907  df-iin 4908  df-br 5053  df-opab 5115  df-mpt 5133  df-id 5447  df-xp 5548  df-rel 5549  df-cnv 5550  df-co 5551  df-dm 5552  df-rn 5553  df-res 5554  df-ima 5555  df-iota 6302  df-fun 6345  df-fn 6346  df-f 6347  df-f1 6348  df-fo 6349  df-f1o 6350  df-fv 6351  df-riota 7107  df-ov 7152  df-oprab 7153  df-mpo 7154  df-1st 7684  df-2nd 7685  df-proset 17538  df-poset 17556  df-plt 17568  df-lub 17584  df-glb 17585  df-join 17586  df-meet 17587  df-p0 17649  df-p1 17650  df-lat 17656  df-clat 17718  df-oposet 36417  df-ol 36419  df-oml 36420  df-covers 36507  df-ats 36508  df-atl 36539  df-cvlat 36563  df-hlat 36592  df-psubsp 36744  df-pmap 36745  df-padd 37037  df-lhyp 37229
This theorem is referenced by:  cdleme22g  37589
  Copyright terms: Public domain W3C validator