Island where all inhabitants are either "knights" who always tell the truth or "knaves" who always lie. Man in green says, "the man in yellow is a knave" Man in yellow says, "we are both knights" Green is a knights and yellow is a knave true. Green is a knave and yellow is a knight. Declarative: communicate statements associated with values (true/ false) 2 clowns stand at a fork; one is knight and the other is knave; one path leads to certain doom. Ask a single yes/ no question to determine which path is safe. Essentially equivalent to asking truth value question associated with declarative statement. Question: would the other clown tell me your path leads to safety (and not certain doom) Doom | safety doom | safety safety | doom safety | doom. Knight | knave knave | knight knight | knave knave | knight. Do not need to know which is knight and which is knave.