FRA, the Swedish government agency for radio communications posts some riddles every year around Christmas. With one you got a couple of phone call logs and wer

FRA, the Swedish government agency for radio communications posts some riddles every year around Christmas. With one you got a couple of phone call logs and were asked questions about who was who in a terrorist group. Plotted the calls with graphviz and the questions were instantly trivial to solve. Great tool with many applications.