In mathematics, a degenerate case is a limiting case in which a class of object changes its nature so as to belong to another, usually simpler, class.
For any non-empty subset of the indices a bounded, axis-aligned degenerate rectangle is a subset of of the following form:
where and are constant (with for all ). The number of degenerate sides of is the number of elements of the subset . Thus, there may be as few as one degenerate "side" or as many as (in which case reduces to a singleton point).