Here's the riddle. I need the answer please.

A person was traveling and he found 2 people on the street.

Person A told the traveler that he's the truthteller and the traveler

asked person B if A was telling the truth. B said A was telling

the truth and that he was a truthteller as well.

They are either both truthtellers or liars.

The answer is that they are both truthtellers but I don't know the

explanation.