In a complex middlegame, it can sometimes be difficult to evaluate positions based on sheer calculation. This is where small positional ideas like the block and lune pawn microstructures can help find the right move. What is going on in this position?
Material is even, with only rooks and pawns on the board, so open files will be critical. Black has one rook tied down to stopping the f7-pawn, and stands worse. White wants to open files in order to exchange both rooks (or just the f8-rook) and promote. Black wants to keep the position closed and draw.
The pawn situations on the a-, b-, g- and h-files are still fluid for the moment. White is threatening to set up two lunes with b5 or g5. Black needs to recognise this as a threat and act quickly.1....h6!1...h6! sets up a block on the kingside. This keeps the g- and h-files firmly closed. It also prevents white's bigger threat of g5! and opening the kingside, either getting an open h-file or a passed pawn, both of which would quickly end the game.1...a6?2.g5!If black does nothing significant or makes a block on the wrong side, white makes a lune on the kingside with 2. g5!. Now black will suffer the kingside opening.Ra73.h5Kc84.hxg6Re75.g6hxg66.Rh8Rd77.Rxf8Rxf78.Ke2+−White wins this rook-for-pawn endgame.1...e5?This attempt to blow up the centre and get counterplay doesn't work.2.g5!The lune.exd43.h5Kc7(3...Rc84.hxg6d45.Rh6Rc66.Rd6+Rxd67.Ke2Kc78.g6hxg69.Rh1d3+10.Kd2Re811.fxe8=Q+−White wins this endgame.)4.hxg6Rfe85.Rh6Re66.f8=QRxf87.Rxe6+−White wins this endgame.2.b5...White sets up the queenside lune, else black will play 2...a6 with another block then shuffling about for a draw.2....a5!Black seals off the queenside, forcing an en passant capture.3.bxa6...3.h5g54.Re1e55.dxe5Ra76.Re5Kc8White cannot make progress except by sacrificing a rook for a pawn, after having manoeuvred all pieces to their optimal locations. Even then black will be able to get at least one rook in to force a perpetual check.3....Ra3!=Black "mines" b1, and white cannot make progress. If at some point Rb1 is played, black has ...Rxa2 followed by ...Rxf7, and white has nothing better then perpetual check, down rook for two pawns. See the example continuations.4.Ke2...4.h5g55.Re1e56.dxe5b57.Re5Kc7White has no entrance, the attacked pawns on f7 and a2 preventing white's rooks from using the squares they really want to.4....Kc75.Rb1Rxa26.Ra1Rxf77.Ra7+Kd8White should take the perpetual. Black will also be careful to keep the king close to the kingside pawns to avoid any passed pawn tricks with Rxg6 or Rxh6.