Ullman- TOC- NFA

Question

The set of strings in (0+1)* such that some

 two O's are separated by a string whose

length is 4i, for some i≥ 0.

Comments

Regular expression for this language can be written as $(0)^{*}+(1)^{*}+0(1)^{*}+(0(1111)^{+}0)^{*}$

---

1* - that means 11 is possible. - you can't find some two 0's which are separated by a string whose length is 4i. i>=0.

 

$(0+1)^*.0.[(0+1)(0+1)(0+1)(0+1)]^*.0.(0+1)^*$ - there are atleast one pair of 0, which are separated by a string with length 4

---

Ohh right sir, I was by mistakenly considering for all 0's instead of some 0's