Members of the Smith family are day-knights and members of the Jones family are night-knights.
Three inhabitants Al, Ben and Cal approach a visitor to the island. It is known that precisely two of them are members of the Jones family and the remaining one is a member of the Smith family.
Al: Ben belongs to the Jones family. Ben: Cal belongs to the Jones family. Cal: Alís surname is Smith.What are the surnames of the three inhabitants? Is it day or night?