2 some 2D geometrical concepts
16 Offset operator+(Offset o)const {
22 Offset operator+=(Offset o) {
27 Offset(Real ix , Real iy) {
41 void translate(Real t) {
46 void unite(Interval h) {
54 bool empty() { return min > max; }
58 Interval(Real m, Real M) {
65 /// a 4-tuple of #Real#s
69 void translate(Offset o) {
79 Box(Interval ix, Interval iy);