Board Thread:The Panopticon/@comment-7302713-20130404114052/@comment-7302713-20130404122125

But saying he never shows up in the right order doesn't mean that she doesn't know his personal order.

If River and the 10th Doctor did do the Picnic at Asgard, or rather anything in fact, she would have done diaries with him and realized that this was a Doctor who hadn't done the Byzantium.

River knows the face of the Doctor who did the Byzantium. So when she meets a Doctor with a different face there are only two options. He's either a younger Doctor (one of 1-10) or he's an older doctor (one of 12-??). So a Doctor who hasn't done the Byzantium and has a different face must be a younger Doctor.

So when River asks the Doctor if they've done the Byzantium and he's completely clueless, she moves on to Asgard. If she's eliminated 11-? with the Byzantium question she'd have to go to something from 1-10.

She wouldn't ask about Asgard if 11 did Asgard. Or any later version. That would be silly. She's looking at events from his early days, not hers. But if she'd done Asgard with 10, then she'd already know that the Doctor with that face was younger than 11.

It's a catch-22.

Either River asks about Asgard knowing that the Doctor can't possibly have done it. Or she asks about the Byzantium knowing that he couldn't possibly have done it.

If she knows that the man who did Asgard had the same face as the man who did the Byzantium then she only needs to ask about one. If they have different faces then she didn't need to ask about the Byzantium because she already has.