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inductive

LogicNat

definition
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module
IndisputableMonolith.Foundation.ArithmeticFromLogic
domain
Foundation
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66 · github
papers citing
422 papers (below)

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IndisputableMonolith.Foundation.ArithmeticFromLogic on GitHub at line 66.

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  63generator. The two-constructor structure mirrors the orbit
  64{1, γ, γ², γ³, ...} as the smallest subset of ℝ₊ closed under
  65multiplication by γ and containing 1. -/
  66inductive LogicNat : Type
  67  | identity : LogicNat
  68  | step     : LogicNat → LogicNat
  69  deriving DecidableEq, Repr
  70
  71namespace LogicNat
  72
  73/-! ## 2. Zero and Successor (Peano Primitives) -/
  74
  75/-- Zero is the identity comparison: a thing compared with itself,
  76costing zero in J. -/
  77@[simp] def zero : LogicNat := .identity
  78
  79/-- Successor is one more application of the generator. -/
  80@[simp] def succ (n : LogicNat) : LogicNat := .step n
  81
  82/-! ## 3. Peano Axioms as Theorems
  83
  84Each axiom is a theorem of the inductive structure. None is posited.
  85-/
  86
  87/-- **Peano P1 (zero is not a successor)**: the identity is
  88distinguishable from any iterate of the generator. -/
  89theorem zero_ne_succ (n : LogicNat) : zero ≠ succ n := by
  90  intro h; cases h
  91
  92/-- **Peano P1, contrapositive**: every successor differs from zero. -/
  93theorem succ_ne_zero (n : LogicNat) : succ n ≠ zero := by
  94  intro h; cases h
  95
  96/-- **Peano P2 (successor injectivity)**: forced by the constructor