Question $3$

Is the following language over $=\{0,1\}$ regular or not? Prove your answer.

$L_3=\{w$ : the substring $10$ occurs exactly $as$ often $inwas$ the substring $01\}$

$($An example of a string in the language is $010$ because there is one occurrence of the substring $01$ and one

occurrence of the substring $10.$ An example of a string NOT in the language is $0101$ because there are two

occurrences of the substring $01$ but only one occurrence of the substring $10.)$