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Theorem dath 36944
Description: Desargues's theorem of projective geometry (proved for a Hilbert lattice). Assume each triple of atoms (points) 𝑃𝑄𝑅 and 𝑆𝑇𝑈 forms a triangle (i.e. determines a plane). Assume that lines 𝑃𝑆, 𝑄𝑇, and 𝑅𝑈 meet at a "center of perspectivity" 𝐶. (We also assume that 𝐶 is not on any of the 6 lines forming the two triangles.) Then the atoms 𝐷 = (𝑃 𝑄) (𝑆 𝑇), 𝐸 = (𝑄 𝑅) (𝑇 𝑈), 𝐹 = (𝑅 𝑃) (𝑈 𝑆) are colinear, forming an "axis of perspectivity".

Our proof roughly follows Theorem 2.7.1, p. 78 in Beutelspacher and Rosenbaum, Projective Geometry: From Foundations to Applications, Cambridge University Press (1988). Unlike them, we do not assume that 𝐶 is an atom to make this theorem slightly more general for easier future use. However, we prove that 𝐶 must be an atom in dalemcea 36868.

For a visual demonstration, see the "Desargues's theorem" applet at http://www.dynamicgeometry.com/JavaSketchpad/Gallery.html 36868. The points I, J, and K there define the axis of perspectivity.

See theorem dalaw 37094 for Desargues's law, which eliminates all of the preconditions on the atoms except for central perspectivity. This is Metamath 100 proof #87. (Contributed by NM, 20-Aug-2012.)

Hypotheses
Ref Expression
dath.b 𝐵 = (Base‘𝐾)
dath.l = (le‘𝐾)
dath.j = (join‘𝐾)
dath.a 𝐴 = (Atoms‘𝐾)
dath.m = (meet‘𝐾)
dath.o 𝑂 = (LPlanes‘𝐾)
dath.d 𝐷 = ((𝑃 𝑄) (𝑆 𝑇))
dath.e 𝐸 = ((𝑄 𝑅) (𝑇 𝑈))
dath.f 𝐹 = ((𝑅 𝑃) (𝑈 𝑆))
Assertion
Ref Expression
dath ((((𝐾 ∈ HL ∧ 𝐶𝐵) ∧ (𝑃𝐴𝑄𝐴𝑅𝐴) ∧ (𝑆𝐴𝑇𝐴𝑈𝐴)) ∧ (((𝑃 𝑄) 𝑅) ∈ 𝑂 ∧ ((𝑆 𝑇) 𝑈) ∈ 𝑂) ∧ ((¬ 𝐶 (𝑃 𝑄) ∧ ¬ 𝐶 (𝑄 𝑅) ∧ ¬ 𝐶 (𝑅 𝑃)) ∧ (¬ 𝐶 (𝑆 𝑇) ∧ ¬ 𝐶 (𝑇 𝑈) ∧ ¬ 𝐶 (𝑈 𝑆)) ∧ (𝐶 (𝑃 𝑆) ∧ 𝐶 (𝑄 𝑇) ∧ 𝐶 (𝑅 𝑈)))) → 𝐹 (𝐷 𝐸))

Proof of Theorem dath
StepHypRef Expression
1 dath.b . . . . . 6 𝐵 = (Base‘𝐾)
21eleq2i 2907 . . . . 5 (𝐶𝐵𝐶 ∈ (Base‘𝐾))
32anbi2i 625 . . . 4 ((𝐾 ∈ HL ∧ 𝐶𝐵) ↔ (𝐾 ∈ HL ∧ 𝐶 ∈ (Base‘𝐾)))
433anbi1i 1154 . . 3 (((𝐾 ∈ HL ∧ 𝐶𝐵) ∧ (𝑃𝐴𝑄𝐴𝑅𝐴) ∧ (𝑆𝐴𝑇𝐴𝑈𝐴)) ↔ ((𝐾 ∈ HL ∧ 𝐶 ∈ (Base‘𝐾)) ∧ (𝑃𝐴𝑄𝐴𝑅𝐴) ∧ (𝑆𝐴𝑇𝐴𝑈𝐴)))
543anbi1i 1154 . 2 ((((𝐾 ∈ HL ∧ 𝐶𝐵) ∧ (𝑃𝐴𝑄𝐴𝑅𝐴) ∧ (𝑆𝐴𝑇𝐴𝑈𝐴)) ∧ (((𝑃 𝑄) 𝑅) ∈ 𝑂 ∧ ((𝑆 𝑇) 𝑈) ∈ 𝑂) ∧ ((¬ 𝐶 (𝑃 𝑄) ∧ ¬ 𝐶 (𝑄 𝑅) ∧ ¬ 𝐶 (𝑅 𝑃)) ∧ (¬ 𝐶 (𝑆 𝑇) ∧ ¬ 𝐶 (𝑇 𝑈) ∧ ¬ 𝐶 (𝑈 𝑆)) ∧ (𝐶 (𝑃 𝑆) ∧ 𝐶 (𝑄 𝑇) ∧ 𝐶 (𝑅 𝑈)))) ↔ (((𝐾 ∈ HL ∧ 𝐶 ∈ (Base‘𝐾)) ∧ (𝑃𝐴𝑄𝐴𝑅𝐴) ∧ (𝑆𝐴𝑇𝐴𝑈𝐴)) ∧ (((𝑃 𝑄) 𝑅) ∈ 𝑂 ∧ ((𝑆 𝑇) 𝑈) ∈ 𝑂) ∧ ((¬ 𝐶 (𝑃 𝑄) ∧ ¬ 𝐶 (𝑄 𝑅) ∧ ¬ 𝐶 (𝑅 𝑃)) ∧ (¬ 𝐶 (𝑆 𝑇) ∧ ¬ 𝐶 (𝑇 𝑈) ∧ ¬ 𝐶 (𝑈 𝑆)) ∧ (𝐶 (𝑃 𝑆) ∧ 𝐶 (𝑄 𝑇) ∧ 𝐶 (𝑅 𝑈)))))
6 dath.l . 2 = (le‘𝐾)
7 dath.j . 2 = (join‘𝐾)
8 dath.a . 2 𝐴 = (Atoms‘𝐾)
9 dath.m . 2 = (meet‘𝐾)
10 dath.o . 2 𝑂 = (LPlanes‘𝐾)
11 eqid 2824 . 2 ((𝑃 𝑄) 𝑅) = ((𝑃 𝑄) 𝑅)
12 eqid 2824 . 2 ((𝑆 𝑇) 𝑈) = ((𝑆 𝑇) 𝑈)
13 dath.d . 2 𝐷 = ((𝑃 𝑄) (𝑆 𝑇))
14 dath.e . 2 𝐸 = ((𝑄 𝑅) (𝑇 𝑈))
15 dath.f . 2 𝐹 = ((𝑅 𝑃) (𝑈 𝑆))
165, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15dalem63 36943 1 ((((𝐾 ∈ HL ∧ 𝐶𝐵) ∧ (𝑃𝐴𝑄𝐴𝑅𝐴) ∧ (𝑆𝐴𝑇𝐴𝑈𝐴)) ∧ (((𝑃 𝑄) 𝑅) ∈ 𝑂 ∧ ((𝑆 𝑇) 𝑈) ∈ 𝑂) ∧ ((¬ 𝐶 (𝑃 𝑄) ∧ ¬ 𝐶 (𝑄 𝑅) ∧ ¬ 𝐶 (𝑅 𝑃)) ∧ (¬ 𝐶 (𝑆 𝑇) ∧ ¬ 𝐶 (𝑇 𝑈) ∧ ¬ 𝐶 (𝑈 𝑆)) ∧ (𝐶 (𝑃 𝑆) ∧ 𝐶 (𝑄 𝑇) ∧ 𝐶 (𝑅 𝑈)))) → 𝐹 (𝐷 𝐸))
Colors of variables: wff setvar class
Syntax hints:  ¬ wn 3  wi 4  wa 399  w3a 1084   = wceq 1538  wcel 2115   class class class wbr 5053  cfv 6344  (class class class)co 7146  Basecbs 16481  lecple 16570  joincjn 17552  meetcmee 17553  Atomscatm 36471  HLchlt 36558  LPlanesclpl 36700
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 5177  ax-sep 5190  ax-nul 5197  ax-pow 5254  ax-pr 5318  ax-un 7452
This theorem depends on definitions:  df-bi 210  df-an 400  df-or 845  df-3or 1085  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 4826  df-iun 4908  df-br 5054  df-opab 5116  df-mpt 5134  df-id 5448  df-xp 5549  df-rel 5550  df-cnv 5551  df-co 5552  df-dm 5553  df-rn 5554  df-res 5555  df-ima 5556  df-iota 6303  df-fun 6346  df-fn 6347  df-f 6348  df-f1 6349  df-fo 6350  df-f1o 6351  df-fv 6352  df-riota 7104  df-ov 7149  df-oprab 7150  df-proset 17536  df-poset 17554  df-plt 17566  df-lub 17582  df-glb 17583  df-join 17584  df-meet 17585  df-p0 17647  df-p1 17648  df-lat 17654  df-clat 17716  df-oposet 36384  df-ol 36386  df-oml 36387  df-covers 36474  df-ats 36475  df-atl 36506  df-cvlat 36530  df-hlat 36559  df-llines 36706  df-lplanes 36707  df-lvols 36708
This theorem is referenced by:  dath2  36945
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