CSCI 2670
Introduction to Theory of
Computing
September 15, 2005

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Agenda
• Yesterday
– Introduce context-free grammars
• Today
– No quiz!
• Quiz postponed until Monday
–
Regular expressions, pumping lemma, CFG’s
– Build CFG’s

Context-free grammar definition
•
A context-free grammar is a 4-tuple
(V,
Σ
,R,S), where
1.
V is a finite set called the
variables
,
2.
Σ
is a finite set, disjoint from V, called
the
terminals
,
3.
R is a finite set of
rules
, with each rule
being a variable and a string of
variables and terminals, and
4.
S
∈
V is the
start variable
.

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