In
logic, especially as applied in
mathematics, concept is a
special case or
specialization of concept precisely if every instance of is also an instance of but not vice versa, or equivalently, if is a
generalization of . A
limiting case is a type of special case which is arrived at by taking some aspect of the concept to the extreme of what is permitted in the general case. A
degenerate case is a special case which is in some way qualitatively different from almost all of the cases allowed.