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## Geometric Objects and Relations

Here are some useful geometric objects and relations.

1. Two dimensional objects--regions including chambers. We have already discussed them.
2. One dimensional objects--segments and walls. A segment is a surface over which lemmings can walk. Mostly we are concerned with segments bounded by walls or drop-offs or other impediment to walkers. However, segments bounded by being above a hill at a lower level may need to be an object because digging in that segment has a different result than digging elsewhere.

On walls useful segments are bounded by overhangs as well as floors and ceilings, because climbers can't climb overhangs.

3. Bridges and segments of bridges require special treatment, because they are dynamic until completed. Even when it is complete, it is sometimes necessary to break a bridge into two segments using a digger.
4. The adjacency relations and containment relations among geometric objects are used.

John McCarthy
Mon Mar 2 16:21:50 PDT 1998