Sets and Matrices - Northeastern University

Let A and B be sets. The two sets are disjoint if their intersection is the empty set. A B Cardinality of sets Inclusion-Exclusion Principle We frequently want too know how many items are in groups. Note that jAj+ jBjcounts all the elements in only A once, and all the elements in only B once. BUT, it counts the elements in A and B TWICE. ................
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