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Title: Automata (theory of computation)
Description: ardens theorem one of the important for automata.

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ARDEN'S THEOREM
http://www
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com/automata_theory/ardens_theorem
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com

Arden's Theorem
In order to find out a regular expression of a Finite Automaton, we use Arden’s Theorem along with
the properties of regular expressions
...

If P does not contain null string, then R = Q + RP has a unique solution that is R =
QP*
Proof −
R = Q + Q + RPP [After putting the value R = Q + RP]
= Q + QP + RPP
When we put the value of R recursively again and again, we get the following equation −
R = Q + QP + QP2 + QP3 …
...
)
R = QP* [As P* represents (ε + P + P2 + P3 + …
...


Assumptions for Applying Arden’s Theorem −
The transition diagram must not have NULL transitions
It must have only one initial state

Method
Step 1 − Create equations as the following form for all the states of the DFA having n states with
initial state q1
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The equations for the three states q1 , q2 , and q

3

q1 = q1 a + q3 a + ε

are as follows −

(ε move is because q1 is the initial state0

q2 = q1 b + q2 b + q3 b
q3 = q2 a
Now, we will solve these three equations −
q2 = q1 b + q2 b + q3 b
= q1 b + q2 b + (q2 a)b

(Substituting value of q3 )

= q1 b + q2 b + ab
= q1 b b + ab*

ApplyingArden ′ sTheorem

q1 = q1 a + q3 a + ε
= q1 a + q2 aa + ε
= q1 a + q1 b(b + ab*)aa + ε

(Substituting value of q3 )
(Substituting value of q2 )

= q1 a + b(b + ab*aa) + ε
= ε a + b(b + ab*aa)*
= a + b(b + ab*aa)*
Hence, the regular expression is a + b(b + ab*aa)*
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Title: Automata (theory of computation)
Description: ardens theorem one of the important for automata.