a simple polygon through all the points
... that a simple polygon through all the points of a three-by-three grid must pass straight through some of the points, rather than turning at each of them?
... that <b id="mwBCA"><a href="./Polygonalization" id="mwBCE" rel="mw:WikiLink" title="Polygonalization">a simple polygon through all the points</a></b> of a three-by-three grid must pass straight through some of the points, rather than turning at each of them?