<div class="user_solution"><div>a)</div><div>1. Ka2? <i>A</i> (2. Qd1 <i>C</i> Kxb4 3. Qc1 Ka5 4. Qa3#)</div><div>1. ... Kc2!</div><div><br /></div><div><b>1. Qd5!</b> <i>B</i> Kxb4 2. Kb2 (3. Qd6+ Ka5 4. Qa3#) Ka5 3. Qxe5 Kb4 4. Qc3#</div><div><br /></div><div>1. Qd1? <i>C</i> (2. Ka2 <i>A</i> (threat reversal in tries) Kxb4 3. Qc1 Ka5 4. Qa3#)</div><div>1. ... Kxb4! 2. Qc2? Ka3 3. Qc3 b4 4. Qb2#</div><div>2. ... Ka5!</div><div>2. Qc1? (3. Ka2 Ka5 4. Qa3#)</div><div>2. ... Kxb3!</div><div>2. Kb2? (3. Qd6+ Ka5 4. Qa3#) Ka5 3. Qa1+ Kb4 4. Qa3#</div><div>2. ... <span style="font-size: 12pt; line-height: 107%; font-family: &quot;Times New Roman&quot;, serif;"></span>Kc5!</div><div><br /></div><div>b)</div><div>1. Qd5? <i>B</i> Kxb4 2. Kb2? (3. Qd6+ Ka5 4. Qa3#) Ka5! 3. Qxe5 Kb4 4. Qc3#</div><div>3. ... Ka6!</div><div>2. Kc2? (3. Qd6+ Ka5 4. Qa3#) Ka3 3. Qxb5 Ka2 4. Qa4#</div><div>2. ... Ka5!</div><div><br /></div><div><b>1. Ka2!</b> <i>A</i> (characteristic twins) (2. Qd1 <i>C</i> Kxb4 3. Qc1 Ka5 4. Qa3#) Kc2 2. Rxb5 Kc3 3. Rd5 Kc2/b5 4. Qc7/Qc5#</div><div>2. ... Kc1 3. Rd5 (4. Qc7#)</div><div><br /></div><div>1. Qd1? <i>C</i> (2. Ka2 <i>A</i> (threat reversal) Kxb4 3. Qc1 Ka5 4. Qa3#, 2. Qe1+ Kd3 3. Rxb5 Kd4 4. Rd5#)</div><div>1. ... Kxb4! 2. Qc2? Ka3 3. Qc3 b4 4. Qb2#</div><div>2. ... Ka5!</div><div>2. Qc1? (3. Ka2 Ka5 4. Qa3#)</div><div>2. ... Kxb3!</div><div>2. Kb2? (3. Qd6+ Ka5 4. Qa3#) Ka5 3. Qa1+ Kb4 4. Qa3#</div><div>2. ... Kc5!</div><div><br /></div><div>Keywords: twin (characteristic), sequence reversal II (threat reversal), stalemate dissolution, flight giving key, sacrifice key (a), sacrifice of white pieces, passive sacrifice, selfblock, remote selfblock, selfpinning</div></div><br />