module StraightSkeleton::InteriorNode

def <=>(other)
  (@travel <=> other.travel) * @nodes.direction
end

def insert!
  @normals = @neighbours.map.with_index do |neighbour, index|
    neighbour.neighbours[1-index] = self if neighbour
    neighbour.normals[1-index] if neighbour
  end
  @nodes.insert self
end