I gave a presentation to MCQLL, on an an example of the duality of generative systems and constraint-based systems. The particular example I discussed was a proof of the equivalence in expressive power between Finite state automata (FSA) and monadic second order logic (with a successor function; MSOL[S]). That is, I presented the proof that any language for which there exists an FSA can be described equivalently using constraints written in MSOL[S].

My slides are here.