code: func (r Rectangle) Contains(p Vec3) bool {
  	return r.Min[0] <= p[0] && p[0] < r.Max[0] &&
  		r.Min[1] <= p[1] && p[1] < r.Max[1] &&
  		r.Min[2] <= p[2] && p[2] < r.Max[2]
  }
docs: // Contains reports whether rectangle r contains point p