From: sspa...@aol.com (SSpanke)
Subject: Re: 0 to Many relationship - Semantic Conceptual Modelling
Date: 1998/09/14
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For what its worth, here's the Null Set Theory:

If A and B are two subsets of a set S, the elements found in A or in B or in
both form a subset of S called the union of A and B, written A È B. The
elements common to A and B form a subset of S called the intersection of A and
B, written A Ç B. If A and B have no elements in common, the intersection is
empty; it is convenient, however, to think of the intersection as a set,
designated by Æ and called the empty, or null, set.