           else
             mesh.edges_vertices.push [v2, v1]
           mesh.edges_faces.push [null, null]
+          # First instance of edge might be on boundary
           mesh.edges_assignment.push 'B'
         if v1 <= v2
           mesh.edges_faces[edge][0] = face

          key = "#{v2},#{v1}"
        if key of edgeMap
          edge = edgeMap[key]
        else
          edge = edgeMap[key] = mesh.edges_vertices.length
          if v1 <= v2

convert.faces_vertices_to_edges = (mesh) ->
  ###
  Given a FOLD object with just `faces_vertices`, automatically fills in
  `edges_vertices`, `edges_faces`, `faces_edges`, and `edges_assignment`
  (indicating which edges are boundary with 'B').
  ###
  mesh.edges_vertices = []
  mesh.edges_faces = []
