old_contents: from halfedge_mesh import HalfedgeMesh
  from halfedge_mesh import Vertex
  from halfedge_mesh import Halfedge
  from halfedge_mesh import Facet
  from halfedge_mesh import norm
  from halfedge_mesh import normalize
  from halfedge_mesh import dot
  from halfedge_mesh import cross_product
  from halfedge_mesh import make_iterable
  from halfedge_mesh import allclose
  
new_contents: from halfedge_mesh import HalfedgeMesh
  from halfedge_mesh import Vertex
  from halfedge_mesh import Halfedge
  from halfedge_mesh import Facet
  from halfedge_mesh import norm
  from halfedge_mesh import normalize
  from halfedge_mesh import dot
  from halfedge_mesh import cross_product
  from halfedge_mesh import make_iterable
  from halfedge_mesh import allclose
  from halfedge_mesh import create_vector
  
subject: Add create_vector to __init__