# Limitations of Regular Expressions

Parentheses in expressions, statement blocks

{{}{{{}{}}{}}}{}{{}{}}

The language of balanced (matched) parentheses (here: curly braces)

- at each point count number of open minus number of closed parantheses
- at every point the number must be non-negative
- at the end the number must be zero

Is there a **finite** automaton describing balenced parentheses?

- I wrote a finite state machine with 10'000 states and it seems to recognize balanced parantheses
- Do I have a bug in my finite state machine? If so, can you tell me how to find it?