This riddle's really really hard?

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There are three persons, John, Peter and his wife Sarah. One of them always lies, the other is always honest. The third always tells the truth after a lie, and lies after telling a truth; however, the credibility of that person's first answer is unknown.

Taking into consideration that you have three questions to ask, each to one person of them, and that you can ask the same person more than one question, what questions should you ask, and to whom, if you want to know who is who?
 
Easy:

Ask one male person (let's call him Person A): "Are you Sarah?"

If he says No, he is always telling the truth; if he says Yes, he is always telling a lie, because a guy can't be Sarah.

If Person A says "Yes", he is always going to lie. So ask him, "Are you John?" If he says YES to this, he is NOT, and therefore, person A is Peter. If he says NO to this, then he IS John, therefore person A is John.

If Person A says "No" to the "Are you Sarah question", he is NOT going to lie. So ask him, "Are you John?" If he says NO to this, he is NOT John, and therefore person A is Peter. If he says YES to this, then he IS John, and therefore person A is John.

Get it?
 
I would ask each one a personal fact after contacting a family member, like is your favorite color purple or something like that.
 
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