static DoubleEdge scaleDoubleEdge(DoubleEdge e, double factor) {
  ret e == null ?: DoubleEdge(scaleDoublePt(e.a(), factor), scaleDoublePt(e.b(), factor));
}

static DoubleEdge scaleDoubleEdge(double factor, DoubleEdge e) {
  ret scaleDoubleEdge(e, factor);
}