- #1

Crystal037

- 167

- 7

- Homework Statement
- Find the regular expression to accept strings following the conditions given below:

(i)strings of a's and b's such that every block of 4 consecutive symbols contains at least 2 a's

(i)strings of a's and b's whose length is either even or a multiple of 3 or both

- Relevant Equations
- I will use E to denote epsilon that is empty string

In first part,since every block of 4 consecutive symbol contain at least 2 a's

The answer in notes is given

(aa(a+b)(a+b)+a(a+b)a(a+b)+a(a+b)(a+b)a+(a+b)aa(a+b)+(a+b)a(a+b)a+(a+b)(a+b)aa)

But this wont be true since if we choose aabbbbaa which is possible according to the above regular expression, it wont be correct since there's a block with 4 consecutive b's

In 2nd part,

I have come up with 2 answers, are both of these same

((a+b)

and ((a+b)

The answer in notes is given

(aa(a+b)(a+b)+a(a+b)a(a+b)+a(a+b)(a+b)a+(a+b)aa(a+b)+(a+b)a(a+b)a+(a+b)(a+b)aa)

^{+}But this wont be true since if we choose aabbbbaa which is possible according to the above regular expression, it wont be correct since there's a block with 4 consecutive b's

In 2nd part,

I have come up with 2 answers, are both of these same

((a+b)

^{2})^{*}+((a+b)^{3})^{*}and ((a+b)

^{2})^{*}*((a+b)^{3})^{*}