Fig. 12.
The classes of formal grammars known as the Chomsky hierarchy (Chomsky, 1957). Each class is a generalisation of the class it encloses, and is more complex than the enclosed classes. Image publicly available under the Creative Commons Attribution-Share Alike 3.0 Unported license (https://commons.wikimedia.org/wiki/File:Wiki_inf_chomskeho_hierarchia.jpg).