L+1 group
An L+1 group is an L group with a leg. The leg can be at the short side or the long side of the L shape. In both cases the group lives or dies according to who has sente.
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First L+1 group
White can kill by playing hane at . This reduces the shape to the standard L group, which we already know is dead.
First L+1 group, hane on one side
The throw-in at no longer works:
jumps and lives. If
makes a placement,
connects, and White cannot connect at a due to shortage of liberties, otherwise Black captures three to make an eye.
However, White can kill by the hane at followed by the placement at
.
tries to live, but
forces
, so
makes a throw in and kills. Note the importance of the
stone.
First L+1 group, hane on both sides
For hundreds of years or even thousands of years, the first L+1 group with hane on both sides is thought to be alive. However, when the group has no external liberties, White can turn it into a ten-thousand year ko.
Black can also get a multi step ko (for white) sequence, which should be better than ten-thousand year ko
Black can get rid of ko threats before continuing. If white wants to continue, he must play yet another ko to force the atari.
Only now does the real ko for the life of the corner start. Black usually should be able to win this or receive ample compensation elsewhere in the steps white took.
Second L+1 group
Second L+1-group, hane one side
The throw-in at doesn't work anymore. Black lives with
: White can not connect at a because Black can capture three to make an eye.
To kill, can go straight to the 2-2 point. After
, Black is dead. See the addendum of the rectangular six in the corner page. As before, the
stone is important.
Second L+1-group, hane on both sides
Second L+1 group, weak leg
The second L+1 group with a weak leg is also unsettled. White can kill at a or Black can live by playing at a.
Something like an L + 1 group
See also: