Each of Monty, Barry, Cal and Pete are inhabitants of this island. It is known that precisely one of them is a knight and the remaining three are liars.
- Monty says, "If Pete and I each have a dog, then exactly one of Barry and Cal has a dog."
- Barry says, "If Cal and I each have a cat, then exactly one of Monty and Pete has a dog."
- Cal says, "If Monty and I each have a dog, then exactly one of Barry and Pete has a cat."
- Pete says, "If Barry and I each have a cat, then exactly one of Barry and I has a dog."
