[wmbwinn]

"but he will have power the Dark Lord knows not"

Dumbledore said that the power Harry has that the Dark Lord knows not is love. I don't think that it should be construed to suggest that maybe Harry is a horcrux and Voldemort doesn't know it.

I suppose that the death of both would satisfy the prophecy. But, the prophecy statement is quite convoluted if that is all that was intended to be meant.

I understand the temptation to think that the connection between Harry and Voldemort on so many levels could be explained by the "Harry is a horcrux" theory. But, I don't think that that theory is the answer. The theory is definitely contradictory to the prophecy. Dumbledore repeatedly said he did not know exactly why or how Voldemort's powers were transferred or copied to Harry. Dumbledore named all of the suspected horcruxes and never said anything that suggested Harry might be one as well.

Maybe Voldemort performed whatever spell is performed to create a horcrux before he entered the Potters' house. Maybe the failure to kill Harry results in the outcome that occurred. Perhaps a confounded horcrux spell is capable of killing or nearly killing the performer of the horcrux spell and transferring power to the survivor. Who knows...