polygon intersection

<svg xmlns="http://www.w3.org/2000/svg" version="1.1">
  <polygon points="35,25 35,35 15,35 15,25 35,25" style="fill:none;stroke:purple;stroke-width:1" />
  <polygon points="50,0 50,40 10,40 10,0 50,0" style="fill:none;stroke:red;stroke-width:1" />
  <polygon points="45,30 45,50 25,50 25,30 45,30" style="fill:none;stroke:blue;stroke-width:1" />
  <polygon points="40,20 40,60  0,60  0,20 40,20" style="fill:none;stroke:green;stroke-width:1" />
</svg>