| Class 3 Problems Death by Blocked Position In Class 3 positions, there is enough material for checkmate, no-one is in danger of getting stalemated, but somehow the units can't get it together. The mechanism to prevent stalemates is the creation of rigid walls made principally of pawns. No other mechanism is known. It is a chess truism that opposing bishops on opposing colour squares lead to a draw. Class 3 is all about this situation. Permanent blocks are set up where White pawns are on White squares say, held up by Black pawns on Black squares. Queens, rooks, knights, and anti-sense bishops can only be present if immobilized. Since so many of the pieces are virtually useless in this Class, we must make the most of what we have, and that's pawns and sense bishops. As long as the position is legal, of course, we regard any number of necessary bishop promotions in the diagram as being artistically irreproachable. The most important pieces are the kings, as the only pieces which have the capability to break down the opposing wall. Fortunately, the kings can be blocked fairly easily. Watch though for leaping escapologist kings, who can retro-bounce to safety... Some problems have stalemates, and can therefore be classed with Class 2 problems also. Most are accidental: instead of wandering indefinitely, one side could give away all its mobile units except for the king, and then get the king blockaded. But sometimes the stalemate prevents a line which otherwise would blow the position open. The classification of blocked positions is into a number of different families according to the main function of the wall(s). If you prefer to be surprised by the ideas a problem contains (and that's not a bad approach), then I might suggest that you click & explore the problems before you read the associated text in which they are embedded. (1) Keep the warring armies apart. 5bk1/4p1p1/4P1P1/7K/8/8/8/8 w - - id #014 (3+4) DR. White to move. Last move? (a) Diagram (b) bKh1; (Expansion of stipulation for Diag 6 from the tutorial.) This one also has a significant Class 2 line. This is a special case of a more general strategy: (2) Divide the mating material, so neither side can be mated. 8/6p1/B4bPk/p3bBpB/P3BbPb/b4BpK/6P1/8 w - - id #040 (10+10) DR. Legal?; (Diag 9 from the tutorial.) 2K2k1N/4pPpP/4P1P1/8/8/1B6/1P6/b7 w - - id #032 (8+4) DR. White to move. Last move?; Black can be stalemated here, but that is not a significant line. 7k/6pP/5bPb/5BbB/4BbBb/5BpB/6Pp/7K w - - id #036 (10+9) DR.Whose move ?; 2B4b/1B6/B4b1b/6p1/5bPk/6pP/Bb4Pp/bB5K w - - id #039 (9+10) DR. White to move. Last move?; The following is another example of this, but the wall serves two other roles as well. Firstly, it keeps selected pieces away from certain areas (i.e. semi-permeable membane), Second, it denies certain mate squares by blocking (i.e. prevent by crime, by not having any dark corners). 5b1N/k1p1pPp1/1pP1P1P1/bP6/1pBK4/1Pp5/2P5/N1b4B w - - id #037 (12+10) DR. White to move. Last move?; There is another theoretical approach which I have not been able to implement yet. This is to force a checkmate to occur on a square such that the checking piece (bishop) is forced to be adjacent to the king, and thus can be captured. (3) Create a narrow enclosure If only the pieces could shuffle round one another... n1k5/P1p1pBp1/1pPbPpP1/1PpKpP2/2P1P3/8/8/8 w - - id #021 (10+10) DR. White to move. Last move?; This one also has a significant Class 2 line. 1K1k1bBR/1p2pPpP/bPp1p1p1/1pP1P1P1/1P3B2/5p2/5P2/8 w - - id #038 (12+11) DR. White to move. Last 3 moves?; Black can be stalemated here, but that is not a significant line. Bb1k1b2/bKp1p1p1/1pP1P1P1/1P6/p5P1/P7/8/8 w - - id #054 (8+9) DR. White to move. Last move?; This one is perhaps one of the harder problems. Stalemate is possible. There are other jobs the walls do, which combine with all the previous roles. For example, they protect pawns from marauding kings: one pawn protects another, but also pawns of both sides keep kings away from vulnerable areas, and they also keep protecting bishops from wandering off. All these are forward reasons for walls. There is also a retro reason. Suppose we have a position which would make an interesting Class 1 problem, but is irretrievably cooked for some reason, typically because uniqueness of uncapturing cannot be enforced. A wall can give some of those pieces an alibi, removing the cook. Whether this is justified or not depends on the quality of the play which is salvaged. (4) Wannabe Class 1 rehabilitated as Class 3 1N1N1b1N/pPpPpPp1/P1P1P1P1/8/8/8/5K2/3B4 w - - id #024 (12+6) DR. J'adoube bK to h1 or h2. White to move. Last move?; Black can be stalemated here, but that is not a significant line. 3b1b2/2pPbPp1/2PpBpP1/3P1P2/8/8/p2R1P2/k1KB4 w - - id #026 (11+9) DR. White to move. Last move?; White or Black can be stalemated here, but that is not a significant line. |