"This used to be a Hall of Mirrors," said the old man, "but the town sold
off the Hall's eight mirrors during the Great Depression." He continued:
"The mirrors were moveable and the Hall could be configured in four
different ways, but this chart is the only remaining record of the
configurations. For each of the four configurations, the chart indicates
where light beams would emerge once shined in from various points. The
mirrors were always set at forty-five degree angles to the walls, as shown
in the example."
"Oh, and I remember one more thing: each square of the Hall was occupied
by a mirror in at most one of the four configurations."