half-factorial ring
An integral domain is called a half-factorial ring (HFD) if it satisfies the following conditions:
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Every nonzero element of that is not a unit can be factored into a product of a finite number of irreducibles.
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If and are two factorizations of the same element into irreducibles, then .
If, in , the irreducibles and are always pairwise associates, then is a factorial ring (UFD).
For example, many orders (http://planetmath.org/OrderInAnAlgebra) in the maximal order of an algebraic number field
are half-factorial rings, e.g. is a HFD but not a UFD (see http://www.math.ndsu.nodak.edu/faculty/coykenda/paper6b.pdfthis paper).