Malcolm: is not easy to spot I think.
is the strongest resistance it seems.
,
are natural. Black then makes the exchange
for
.
serves to prevent White from making a bulky five. After
, Black plays in
leading to the position in the next diagram.
Now it's White's turn. White must prevent Black from playing at a which gives Black a living shape. However a white move at a would give precisely the position that already occurred at the end of Diag. 1.1.
Now if the ruleset has a superko rule, this means that White cannot play at a and so Black lives.
If the ruleset does not have a superko rule, White can play at a. The position can then cycle indefinitely, and is known as an eternal life position.
Malcolm: This position gives White almost unlimited ko threats for ko fights elsewhere.
But if Black blocks at ,
reduces Black's eye space. Black is dead: