Also take a look at the Boom Hierarchy [1], which came from the same era (Bird-Meertens formalism, etc.). It describes relationships between data structures con

Also take a look at the Boom Hierarchy [1], which came from the same era (Bird-Meertens formalism, etc.). It describes relationships between data structures constructed from 4 algebraic properties: unit, commutative, associative and idempotent. The resulting 16 possibilities include the familiar set, bag, list and tree, but also other less useful combinations, such as non-empty mobile. [1] http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.49.3252&rep=rep1&type=pdf http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.49....