def add_face(edges_array)
      edge_array_check(edges_array)
      face = Face.new(edges_array)
      @faces << face
      face
    end
def add_face(edges_array)
      edge_array_check(edges_array)
      face = Face.new(edges_array)
      @faces << face
      face
    end
in addition to its parent's :vertices and :edges
 Contains (inherits)
 attr_accessor :value