code: func (r Rectangle) Inset(n float64) Rectangle {
  	if r.Dx() < 2*n {
  		r.Min.X = (r.Min.X + r.Max.X) / 2
  		r.Max.X = r.Min.X
  	} else {
  		r.Min.X += n
  		r.Max.X -= n
  	}
  	if r.Dy() < 2*n {
  		r.Min.Y = (r.Min.Y + r.Max.Y) / 2
  		r.Max.Y = r.Min.Y
  	} else {
  		r.Min.Y += n
  		r.Max.Y -= n
  	}
  	return r
  }
docs: // Inset returns the rectangle r inset by n, which may be negative. If either
  // of r's dimensions is less than 2*n then an empty rectangle near the center
  // of r will be returned.