The first corona of a Tile is the set of all tiles that have a common boundary point with that tile (including the original tile itself). The second corona is the set of tiles that share a point with something in the first corona, and so on.

**References**

Eppstein, D. ``Heesch's Problem.'' http://www.ics.uci.edu/~eppstein/junkyard/heesch/.

© 1996-9

1999-05-25