Knights and Knaves Puzzle Generator with Not All Statements Determined
This Demonstration provides a generator of "knights and knaves" logic puzzles in which the status of at least one inhabitant is indeterminable. These puzzles are about an island in which some natives called "knights" always tell the truth and others called "knaves" always lie. It is assumed that every inhabitant of the island is either a knight or a knave (but cannot be both). If an inhabitant makes a statement , then we may conclude that is a knight if and only if is true. Such a fact is symbolically represented by .
 R. M. Smullyan, What Is the Name of This Book?, Englewood Cliffs, NJ: Prentice–Hall, 1978.