I heard that some operations involving regexes that do not have common elements can NOT be generated using a finite automata. I do not remember what it was, where it was from, can anyone tell me what that could possibly be?
Edit : I finally managed to find the exact statement. Here it is, below :
A language (like $(00)^n (11)^n$) can not be generated by an FSM since there is no common character in "00" and "11". We need to keep count of both which is not possible with a finite automata as the count can be infinite.