Owen Astrachan Eugene Wallingford Department of Computer Science Department of Computer Science Duke University University of Northern Iowa Durham, NC 27708 Cedar Falls, IA 50614 ola@cs.duke.edu wallingf@cs.uni.edu Copyright © 1998, Owen Astrachan and Eugene Wallingford Permission is granted to make copies for PLoP'98. Background There are many ways to look at patterns. An especially useful way to