Function bet2_vertex_normals 

pub fn bet2_vertex_normals(
    vertices: &[[f64; 3]],
    faces: &[[usize; 3]],
) -> Vec<[f64; 3]>

bet2’s Mpoint::local_normal: the sum of its triangles’ Triangle::normal(), (v2 − v0) × (v1 − v0) (not normalised, so area-weighted), normalised.