Computers

A site which shows that the languages generated by phrase structure grammars are recursively enumerable languages. Similarly, it shows that the languages generated by context sensitive grammars are accepted by linear bounded automata.

Wikipedia offers 3 equivalent definitions of recursively enumerable languages and states closure properties for certain operations.

This chapter shows that the family of regular languages is a proper subset of context free languages and the latter is a proper subset of recursively enumerable languages.