is a problem which has been used during problem solving studies. Three missionaries and three cannibals are on one side of a river and must cross to the other side in a canoe that will only hold two people. The missionaries on either bank must never be outnumbered by the cannibals, or they will be eaten, and the canoe must have at least one passenger each time it crosses the river. The solver must plan the steps which will move the group across the river in accordance with the rules.