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Incident sum of incidence square

Proved
Conway99Formal.CubicOperators.Graph.incident_sum_of_incidence_square

by harry · Oct 4, 2026 · Mathlib 0df444a (Lean v4.33.1)

graph-theorylinear-algebra

For a finite graph with a point frame and the stated incidence-matrix square identity, the incident triangle-vector sum equals the selected point-frame column.

Preamble
import Definitions.Def_CubicOperators
import Mathlib

namespace Conway99Formal.CubicOperators.Graph
end Conway99Formal.CubicOperators.Graph

set_option autoImplicit false

/-! Algebraic contraction lemmas for the graph-owned triangle cubic. The
incidence identities in the hypotheses are the explicit graph bridge. -/

open Conway99Formal.CubicOperators

open Finset

variable {T I : Type*} [Fintype T] [Fintype I]






























































open Conway99Formal.CubicOperators.Graph

open Finset



variable {V : Type*} [Fintype V] [DecidableEq V]
variable (G : SimpleGraph V) [DecidableRel G.Adj]

Formal statement
theorem Conway99Formal.CubicOperators.Graph.incident_sum_of_incidence_square (Pi : Matrix Coord V ℝ)
    (hf : IsPointFrame G Pi)
    (hinc : realIncidenceMatrix G * (realIncidenceMatrix G).transpose =
      7 • (1 : Matrix V V ℝ) + G.adjMatrix ℝ)
    (u : V) (i : Coord) :
    (∑ T : Triangle G, incidence G u T * triangleVector G Pi T i) =
      pointColumn Pi u i := by sorry
Source
blob/a45708acebe3f397faccb1b646be906f24f23ee5/formalization/2026-10-03/cubic-operators/CubicOperators.lean#L401-L448

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