Intersections of lines, for example, remain intersections, and the hole in a torus {doughnut} cannot be transformed away. Thus a doughnut may be transformed topologically into a coffee cup {the hole turning into a handle} but never into a pancake. Topology, then, is really a mathematics of relationships, of unchangeable, or "invariant," patterns.
( Fritjof Capra )
[ The Systems View of Life: A ]
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