pub fn vanishes_at(
model: &Model,
vertex: VertexId,
faces: [FaceId; 2],
) -> GeopResult<bool>Expand description
Whether faces could meet tangentially at vertex, their normals
there parallel: where the edge between them vanishes, the corner
between the faces opening out flat — two equal pipes joined, where
they touch. Its chain ends there, and a blend of it narrows to nothing.