Theory: Difference between revisions

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 ==Formal Languages==
+===Regular Languages===
+* Type 3 of the Chomsky Hierarchy
+* Recognized by finite state machines
+* Closed under union, concatenation, Kleene, intersection, difference, complement, reverse
+===Context-Free Languages (CFLs) / Grammars (CFGs)===
+* Type 2 of the Chomsky Hierarchy, a proper superset of RL's
+* Recognized by nondeterministic pushdown automata
+** Deterministic pushdown automata cannot recognize all CFL's!
+* Closed under union, concatenation, Kleene, reverse
+* Not closed under complement or difference
+* The intersection of an RL and CFL is a CFL, but CFLs are not closed under intersection
 * LL(''n''):
 * LR(''n''):
-===Context-Free Languages (CFLs) / Grammars (CFGs)===
+===Context-Sensitive Languages===
+* Type 1 of the Chomsky Hierarchy, a proper superset of CFL's
+* Recognized by linear bounded automata
+===Recursively-Enumerable Languages (Class [http://qwiki.stanford.edu/wiki/Complexity_Zoo:R#re RE])===
+* Type 0 of the Chomsky Hierarchy, a proper superset of CSL's
+* Recognized by Turing Machines
 [[Category: CS GRE Prep]]