Click here to see the Foxtrot "assignment" on Facebook.

Source code: http://primepuzzle.com/tc/foxtrot.tc

Sample run:

A solution in JavaScript may be found at "Mathspeak."

A far more elegant solution by Amrit Tuladhar (also in JavaScript) may be found at http://www.amrittuladhar.com/projects/foxtrot/ .

Finally, Ken Owen did it in Perl!