Indeed, if you take a word in $S$, and change the first letter according to the rule below, then you get a word not in $S$: OverflowAI: Where Community & AI Come Together, Behind the scenes with the folks building OverflowAI (Ep. You will be notified via email once the article is available for improvement. My cancelled flight caused me to overstay my visa and now my visa application was rejected. Is there any pattern or sequence or algorithm to find this? Example 1: It only takes a minute to sign up. 0 0$). When we see another character, the count flips whether it was even or odd.
number of substrings with each character occurring even times
