Endgame puzzle (hard)

This is our starting position (black to play): primie facie it probably seems like white is winning, up a pawn, and its pretty close to promotion. But then, with that said, we do have oposite coloured bishops, which usually make for drawn endgames. Sure black does have a discovered check, but Ra4+ (all the other rook moves lose the bishop) with Rxa5 doesn't look that promising because of that darn d-pawn.  When I first studied this position (its adapted from a game of mine) I found it surprising that my intuitions were way off the mark: actually, black is winning!

See if you lot can work it out: there are multiple varaitions but i think all roads lead to rome, as the saying goes. The problem is that the puzzle is quite deep and complex, meaning that Rybka constantly reached the "event horizion" and therefore may not have found the best defences.

anyway have a go:   this puzzle gives the line that (i think) gives white the most drawing chances (except for the whites penultimate move, which is a blunder... but it is played because it makes for a good puzzle ), all the other variations are in the diagram below. Some of them are pretty neat, and might need to be looked at just in order to understand puzzle i have set. Hint: this puzzle is all about finding the right idea. get that, and the rest should follow.

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and as promised, all the nitty gritty detail:

Very good, I didn't get the first move at all I played Ra4+ then push up the side. As soon as I saw your first move though I got it. Again great puzzle.

A very cunning plan