During an excursion to the desert at the 2011 ACM-ICPC World Finals, you come across an old Egyptian tomb. Unfortunately, opening the tomb turns out to be a bad idea: all of a sudden, what was just a few moments ago an empty desert has now become a desert crawling with grumpy mummies (you would be grumpy too if you were suddenly awakened after a few thousand years of peaceful sleep).(Fortunately, after solving this problem, you woke up safe and sound in a hotel room in Florida. The enraged mummies had just been a dream.
Or had they?)