Parametrized data types do not need highly constrained parameters

Data types may be considered as objects in any suitable category, and need not necessarily be ordered structures or many-sorted algebras. Arrays may be specified having as parameter any object from a category %plane1D;4A6; with finite products and coproducts, if products distribute over coproducts. The Lehmann-Smith least fixpoint approach to recursively-defined data types is extended by introducing the dual notion of greatest fixpoint, which allows the definition of infinite lists and trees without recourse to domains bearing a partial order structure. Finally, the least fixpoint approach is shown allowing the definition of queues directly in terms of stacks, rather than through a separate equational specification