# Penrose Kites and Darts (3)

When adding Kites and Darts to a pattern, it soon becomes obvious that it is only ever possible to place either a kite or a dart in one position only. ie you cannot 'rotate' a tile; the positioning rules forbid it.

Where the edge of your tiling is fairly convex, you quite often have a choice as to whether to place a kite or a dart. On the other hand, where the edge is sharply reentrant (concave), it is usually only possible to place one of the two tiles.

There are a number of situations in which it is less obvious that a tile is forced and they are illustrated below:

Or to put it another way, if you look at the edge of the flowerpot, you will see that every free vertex is either on the edge of a dis, a superkite or a star.