 
Summary: Theory of Computation
Lecture 8: Pushdown Automata
Max Alekseyev
University of South Carolina
February 7, 2012
Lecture Outline
Pushdown Automata (PDA)
PDA Computation
Equivalence with Contextfree Grammars
Languages with Recursive Structure
Consider a language L = {0n1n  n 0}. As we already know, this
language is not regular, thus it cannot be recognized by an NFA.
Languages with Recursive Structure
Consider a language L = {0n1n  n 0}. As we already know, this
language is not regular, thus it cannot be recognized by an NFA.
However, if we equip NFA with a simplest memory structure
(stack), allowing it to memorize what have been read, it will be
possible to recognize L. Stack is an infinite LIFO (last in, first out)
queue of symbols, allowing pushing (storing at the top of stack)
and popping (reading and removing from the top of stack) one
