Rainer Staudte & Michael Schlosser (Germany)
Twin (a): wKc1
Try: Catching a Knight in try. Try with echo. 1.Sd7+? Kd6! 2.Sb6 (2.Sf6 Ke7!=) 2…Kc7!= One Knight is lost – Echo.
Solution: The key move and the solution result from the knowledge given above.
1.Sa6+! Kb5 (1) 2.Sc7+! Ka4 3.Kb2! (2) White prevents the Black King to enter the drawing zone (squares b2-a2-a1-b1). 3… c5 4.Sd5! c4 5.Sc3+! +- A guarded Knight blockades the c-Pawn on square c3.
(1) 1…Kb6 2.Sb4! Ka5 3.Sa2! Ka4 4.Kb2
(2) 3.Kc2? Ka3! threatens Ka2 and reaches the drawing corner 4.Kb1 c5!
(3) 5.Sd5 c4! 6.Sc3 Kb3! = (3) 4…Kb3? loses after 5.Sde6! threatens Nc5 5…c5 6.Sd5! c4 7.Sd4+ or Nc5+ 7…Ka4 8.Sc3+!
Twin (b): wKc3
Try: Symmetric try, Catching a Knight in try. 1.Se6+? Kd6! 2.Sf4 c5! 3.Kc4 Kc7! Catching a Knight. 4.Sa6+ Kb6 or Kb7; 1.Sd7+? Kd6!
Solution: The Pawn crossed the Troitsky line, but White can blockade him by a Knight securely.
1.Sa6+! Kb6 (1) 2.Sb4! Kc7 (2) 3.Sf7! (3) c5 4.Sd5+! Kc6 5.Kc4!
(1) 1…Kb5 2.Sc7+! Kb6 3.Se8 2.Sb4? c5!
(2) 2…c5 The Pawn is already beyond the Troitsky line, but White can blockade him later by a Knight on c3. 3.Sd5+! Kb5 4.Kc2 or Kb2 c4 3.Sc3+ wins.
(3) 3.Se6+? Kd6! 4.Sf4 c5! 5.Sbd3 c4
• Symmetrical position, asymmetrical solution, mutual zugzwang
• We know from endgame theory: According to Troitsky line White wins if a guarded Knight blockades the c-Pawn on a square at least on c4. If a Knight blockades the Pawn only on square c3 White wins preventing the Black King to enter the drawing zone (squares b2-a2-a1-b1).
• In the main lines of the twins Black Pawn c4 is stopped by Knight on c3 (behind the Troitsky line)