FA-88840 / Mesh topology invariants / Member archive

Adjacent pair count uses interior edges · case 05

Face pairs sharing two edges or fins are miscounted.

Member previewVariant 5 · 3 implementations · 7 checks per implementation

Case contract

Input: polygon faces. Two faces are adjacent when they share an undirected edge (fins give every pair on the edge). Return [distinct adjacent face count per face, number of adjacent face pairs].

Why this case matters

Mesh processing pipelines (remeshing, export, simulation, printing) trust these topological counts and adjacency answers; a wrong invariant silently accepts broken meshes or rejects valid ones.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
book	`[[2, 2, 2], 0]`	`[[2, 2, 2], 3]`	Failed

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