Diagram 1, White invades san-san, now black stone is at third-line as opposed with previous lesson Corner Based 1 – Invasion. If Black plays at B will be inappropriate. Thus, White will play at A. Be informed, in this situation – it is very hard to make unconditional living for White.
Diagram 2, This is the most common KO result for both players. If White wins the KO moving A will make Black thin outside. Vice versa, Black winning the KO at B is very thick.
Diagram 3, In case Black does not like the result of KO, extended at move-1. White is alive when continues from move-2 to move-6. To be informed Black move-1 is also the strongest move and the outcome does not affect much of Black’s thickness outward.
Diagram 4, Black move-3 from Diagram 3 thus must be correctly played. White must play at move-4 to live because White C next creates eyes. White exchanged at A and Black B does not work. Black to kill – where to move next?
Diagram 5, Black move-5 then move-7 forces White to kill at move-8 creates a chance to kill White at A or White to live at A. However, Black is less likely to choose A from this diagram because it takes too much moves (simply to consider KO outside).
Diagram 6, Black move-5 is a killer-move. If Black tries to kill at A, White can simply survive at B.
Diagram 7, White move-6 is a mistake, Black move-9 kills White unconditionally.
Diagram 8, White move-1 is correct and creates KO at move-3. Black is happier to initiate the KO first.
Diagram 9, Without the exchange at A, White best move is replies at move-6 as White initiate the KO first. Notice the KO fight happens at the side which is different from Diagram 2.
Diagram 10, When Black extended at move-1, White cannot lives playing move-2.
Diagram 11, White tries move-3 then extended back at move-7. This is one of the classical Tsumego problem and happened mostly at san-san invasion. The reason why kyu players need to master before reaching shodan. Black to kill.
Diagram 12, “death at hane” and move-14 is a must-know killer move. If White continues at A, Black throws-in B kill.
Diagram 13, in some cases Black move-12 is correct but not here.
Diagram 14, If White extend at move-1 is another tsumego Problem. How to kill?
Diagram 15, If Black move-2 the result is KO here as White can throws-in at A, Black eats at B then C KO.
Diagram 16, Black move-1 removes the eye is correct. White is dead.
Diagram 17, If White needs the KO, move-3 is the key. Black A and White atari at B gives KO. Black move-6 is strongest move trying to kill without KO.
Diagram 18, Black must retreat at move-8, Black A, White B lives.
Diagram 19, White continues to cut and fight from move-9. A is ladder for White. Hence, Black to choose move-8 must consider ladder.
Diagram 20, White move-3 cannot survive unless Black is at A forth-line not third-line.
Diagram 21, Black move-4 then atari at move-6 kills White.
Diagram 22, If Black plays move-4 in this diagram, White lives from move-5 to move-11.