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Logtalk - Object oriented extension to Prolog
Release 2.21.5

Copyright (c) 1998-2004 Paulo Moura.  All Rights Reserved.
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To load all entities in this example compile and load the loader file:

| ?- logtalk_load(loader).

You will need to load the objects in the roots and relations examples.

You will also need to consult the following files in the library directory: 
events_loader, types_loader, metapredicates_loader, and hierarchies_loader.
Alternatively, you may load the library all_loader file to load all library 
entities.

In this example we have several types of polygons that can be concentric.
This is represented by a concentric binary relation ensuring that whenever 
a polygon is moved towards a new position, all polygons likewise concentric 
are moved along with them.