A certain public school superintendent passed down a verbal set of instructions to his assistant concerning the appearance of Halley's Comet a few years back. The superintendent said:

Next Thursday at 10:30 a.m., Halley's Comet will appear over this area. This is an event that occurs only once every 75 years. Call the school principals and have them assemble their teachers and classes on their athletic fields, and explain the phenomena to them. If it rains, then cancel the day's observation and have the classes meet in the auditorium to see a film about the Comet.

The assistant superintendent telephoned the school principals with this message: By order of the superintendent of schools, next Thursday Halley's Comet will appear over your athletic field at 10:30 a.m. If…