# MandysNotes

Monday, 17 March 2014 23:36

## Disjunction and Conjunction

By  Gideon
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Now suppose we consider only animals that are either duck-billed, or are mammals.

This is the set "A or B," the disjunction of A and B, written as:

$A \cup B,$

and illustrated in the following diagram:

This set, $$A \cup B,$$ contains ducklings, and rabbits, and platypuses.

On the other hand, the set of animals that are both duck-billed and are mammals is the set:

"A and B,"

written:

$A \cap B,$

and called the conjuction of A and B.

Note that the set $$A \cap B$$ contains only platypuses.