theorem
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D_physical_compatible
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IndisputableMonolith.Foundation.DimensionForcing on GitHub at line 396.
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393def D_physical : Dimension := 3
394
395/-- D_physical is RS-compatible. -/
396theorem D_physical_compatible : RSCompatibleDimension D_physical := D3_compatible
397
398/-- The eight-tick cycle in D = 3 dimensions. -/
399theorem physical_eight_tick : EightTickFromDimension D_physical = 8 := rfl
400
401/-- **WHY D = 3**
402
403 The dimension is not a free parameter. It is forced by:
404
405 1. **Alexander duality (PRIMARY, proved from axiom)**:
406 `SphereAdmitsCircleLinking D ↔ D = 3`, proved from the reduced
407 cohomology of S¹ axiom in `AlexanderDuality.lean`. Independent of T7.
408 H̃₁(Sᴰ \ S¹) ≅ H̃^{D-2}(S¹), nontrivial iff D = 3.
409
410 2. **Clifford algebra (CHARACTERIZATION)**: Cl₃ ≅ M₂(ℂ) gives
411 2-component complex spinors — the unique structure for spin-½.
412 (See `CliffordBridge.cl3_iso_m2c`)
413
414 3. **Spin group (CHARACTERIZATION)**: Spin(3) ≅ SU(2) is the simplest
415 non-abelian compact Lie group (gauge structure for weak interactions).
416
417 4. **Bott periodicity (CONSEQUENCE)**: Period 8 = 2³ = 2^D follows
418 from D = 3, linking Clifford periodicity to dimension.
419
420 5. **Gap-45 (CONSEQUENCE)**: lcm(8, 45) = 360 = 2³ × 3² × 5 follows
421 from the 8-tick = 2^3 derived from D = 3.
422
423 The Alexander duality argument is the logically primary route.
424 Items 2–5 are consequences or characterizations, not premises. -/
425theorem why_D_equals_3 :
426 -- Spinor structure requires D = 3