Hint

There are four cases in which the predicate menu(Status,X,Y,Z) should be true. For each of them you have to specify a rule. The four cases are

• Status = hungry, X is some starter, Y is some main dish, Z is some desert
• Status = not_so_hungry, X is some starter, Y is some main dish, Z = nothing
• Status = not_so_hungry, X = nothing, Y is some main dish, Z is some desert
• Status = on_diet, X is some starter, Y is some main dish, Z is some desert

Solution

Back to the exercise.