island is added in the middle of the river, then any number of couples can cross using a two-person boat. If crossings from bank to bank are not allowed, then 8n−6 one-way trips are required to ferry n couples across the river;, p. 76 if they are allowed, then 4n+1 trips are required if n exceeds 4, although a minimal solution requires only 16 trips if n equals 4., p. 79. If the jealous couples are replaced by missionaries and cannibals, the number of trips required does not change if crossings from bank to bank are not allowed; if they are however the number of trips decreases to 4n−1, assuming that n is at least 3., p. 81. History The first known appearance of the jealous husbands problem is in the medieval text Propositiones ad Acuendos Juvenes, usually attributed to Alcuin (died 804). In Alcuin's formulation the couples are brothers and sisters, but the constraint is still the same—no woman can be in the company of another man unless her brother is present., p. 74. From the 13th to the 15th century, the problem became known throughout Northern Europe, with the couples now being husbands and wives., pp. 291–293. The problem was later put in the form of masters and valets; the formulation with missionaries and cannibals did not appear until the end of the 19th century., p. 81 Varying the number of couples and the size of the boat was considered at the beginning of the 16th century., p. 296. Cadet de Fontenay considered placing an island in the middle of the river in 1879; this variant of the problem, with a two-person boat, was completely solved by Ian Pressman and David Singmaster in 1989. In 2020, controversy surrounding the racist themes in a cartoon about the problem led the AQA exam board to withdraw a text book containing the problem. See also Wolf, goat and cabbage problem Circumscription (logic) References Logic puzzles