1. M . S C . S / W ( P R E V I O U S )
B Y : G U N J A N G A U R
Automata
2. REGULAR EXPRESSION:
The regular expression are useful for representing
certain sets of strings in an algebraic fashion.
These describe the languages accepted by finite
state automata.
We give a formal recursive definition of regular
expressions over ∑ as follows:
1. Any terminal symbol (that is an element of ∑),Λ
and φ are regular expressions.
2. The union of two regular expressions R1 & R2
written as R1+R2, is also a regular expression.
3. 3. The Concatination of two regular expressions R1 &
R2, written as R1R2, is also a regular expression.
4. The Iteration of regular expressions R, written as
R1*, is also a regular expression.
5. If R is a regular expression, then (R) is also a
regular expression.
6. The regular expression over ∑ are precisely those
obtained recursive by the application of the rule 1-5
once or several time.
