Function mixed

code/geometry/convex_hull3d.cpp:2–2

#include "primitives3d.cpp"
double mixed(P(a), P(b), P(c)) { return a % (b * c); }
bool cmpy(const point3d& a, const point3d& b) {
  if (abs(a.y-b.y) > EPS) return a.y < b.y;
  if (abs(a.x-b.x) > EPS) return a.x < b.x;