Definition of the Chomsky hierarchy

1. Let be a grammar, where N is a set of nonterminal symbols, is a set of terminal symbols, P is a set of rules, and is the start symbol.
2. Let
3. Then G is of Type i (G is a grammar) if P fulfils the ith condition:

   Type 0:

   has the form , with .

   Type 1:

   has the form , with or (note further conditions).

   Type 2:

   has the form , with .

   Type 3:

   Either: has the form , with ,
   or: has the form , with

Task:

Find further explanations of the Chomsky hierarchy in the literature or on the web.