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) {
62 Interval &operator += (Real r) {
70 /// a 4-tuple of #Real#s
74 void translate(Offset o) {
84 Box(Interval ix, Interval iy);