If there is a cephalopod then it is a mollusk. If there is a nautilus then it is a cephalopod. Mollusk-Rule: If there is a mollusk then it is a shellbearer. Cephalopond-Rule: If there is a cephalopod then it is not a shellbearer. Nautilus-Rule: If there is a nautilus then it is a shellbearer. Molly is a mollusk. Sophie is a cephalopod. Natalie is a nautilus. Nautilus-Rule overrides Cephalopond-Rule. Cephalopond-Rule overrides Mollusk-Rule. Nautilus-Rule overrides Mollusk-Rule.