There are 3 missionaries, 3 cannibals, and 1 boat that can carry up to two people on one side of a river.

Goal: Move all the missionaries and cannibals across the river.

Constraint: Missionaries can never be outnumbered by cannibals on either side of the river, or else the missionaries are killed.

State = configuration of missionaries and cannibals and boat on each side of the river.

Operators: Move boat containing some set of occupants across the river (in either direction) to the other side.