U
Union
(of sets) If P and Q are sets the
union of P and Q (written P U Q) is the set of all elements that belong to
P
or belong to Q or belong to both P and Q.
"P U Q" is read "P union Q "
Unique
factorization property Every composite number can be expressed as the
indicated product of prime
factors
in one and only one way, except for the order of the factors