Black to move in this chess position. How should black proceed? This chess endgame is VERY DIFFICULT! This is NOT a one move or simple solution. You need to take time to study this position to see if you can find a win.
Why not follow the convention of showing a1 on the right lower side?
- ... Rb3 is necessary to allow for the necessary tempi gains, this point is clarified if white plays 8. Rg6+ Kf2 9. Rxg2+ Kxg2 and the black king gets to c6 in time (is it clear now why the black rook has to be in the third line? White is forced to capture in g2, otherwise black builds the bridge on the third line) instead of 8. a5.
I think the same strategy doesn't work because the black king and rook can't catch up with the pawn in time to win because the pawn is on a4.
But in your first line, black never needed the rook as a shield- he walks the white rook down after putting his own rook on b1 to support the advance of g1(Q). I am asking why this same strategy doesn't work in the second line after 5.a4.
I think Rb3 is the only winning move because it can shield the black king from checks in the right moment.
And why did it have to be 5.......Rb3! that black had to play? Why does 5.....Rb1 only draw?