Interval y () const{return interval_a_[Y_AXIS]; }
Interval operator[] (Axis a) const;
Interval &operator[] (Axis a);
+
+ Offset center () const;
void translate (Offset o);
/// smallest box enclosing #b#
void set_empty ();
+ void add_point (Offset);
void scale (Real r);
void unite (Box b);
Box ();