This problem involves two people. Person A and person B. They can either always tell the truth, or always lie. When asked, person A replies that: "At least one of us is a liar." Does person A and B tell the truth or do they lie?
What I have so far is that person A can either tell the truth or lie. If he tells the truth, then his statement can be expressed by "A$\lor$B", if he lies then it must be given that they are both speaking the truth, which contradicts that he would be a liar. So person A must be speaking the truth.
But if person A is speaking the truth, then person B could be either lying or speaking the truth. Both would still make person A tell the truth.
So how can I figure out whether person B is speaking the truth or not?