Ok, here's the thinking behind this strange looking move. Firstly, tenuki:
- Click Here To Show Diagram Code
[go]$$Bcm16 Sente Black corner?
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . 3 a . O . . b . . . . . . O O . . |
$$ | . . a X . . . 1 . , . . . O . X . . . |
$$ | . . . . . X . . . . . . . . . . X . . |
$$ | . . C . . . . . . . . . . . . X O . . |
$$ | . . . . . . . . . . . . . . . O X . . |
$$ | . . . . . . . . . . . . . . . . X . . |
$$ | . . C . . . . . . . . . . . . . . . . |
$$ | . . . B . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . W . . . . . . . . . . . . X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . X . O . . . , . . . . . X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]
By playing in the corner (or

at "a") Black simply swallows up almost all of the potential over here, and makes it very easy to kill the White stone at the top to boot. Losing the 3-3 invasion, and having no invasion points on the left side (without armpit nudging anyway, so no thanks!) seems huge to me, and something I can't afford to take lightly. The ability to break into this corner almost disappears with one more Black move, and followups such as "b" make it more and more uncomfortable for White. Not only this, but when Black secures the corner, the marked Black stone on the left becomes a lot stronger, and certainly the marked White stone starts to become weak. Black looks like he may be able to protect the corner in sente, and this is intolerable (or, at least, demonstrates to me that playing in the corner now is pretty urgent for White).
So, why not the 3-3?
- Click Here To Show Diagram Code
[go]$$Bcm16 Sealed in horribly
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . b . . 5 . . . . . . . . . . . |
$$ | . . 2 4 . O . . . . . a . . . O O . . |
$$ | . . 3 X . . . 1 . , . . . O . X . . . |
$$ | . . . . c X c . . . . . . . . . X . . |
$$ | . . . . . . . . . . . . . . . X O . . |
$$ | . . . . . . . . . . . . . . . O X . . |
$$ | . . . . . . . . . . . . . . . . X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . B . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . W . . . . . . . . . . . . X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . X . O . . . , . . . . . X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]
Black can only want to block from this side. sealing White into a small corner and aiming for followup moves at "a" and "b". None of the cuts at "c" look promising for White because Black has all the local strength, and Black can even choose to play

as a tenuki with the remaining large points on the board, and there are lots of unpleasant places to aim at.
So, I have to play in the corner, but I really dislike the 3-3. This probe/invasion is designed to get a feel for Black's desires. Firstly, the stone at the top is a one-point jump away from the crosscut position:
- Click Here To Show Diagram Code
[go]$$Bcm16 Crosscut support
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . 3 4 a O . . . . . . . . . O O . . |
$$ | . . 2 X . . . 1 . , . . . O . X . . . |
$$ | . . . . . X . . . . . . . . . . X . . |
$$ | . . . . . . . . . . . . . . . X O . . |
$$ | . . . . . . . . . . . . . . . O X . . |
$$ | . . . . . . . . . . . . . . . . X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . X . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . O . . . . . . . . . . . . X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . X . O . . . , . . . . . X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]
As such, I am very happy playing the crosscut if Black tries to hane. The fact "a" becomes a wedge rather than a straight atari makes it harder for Black to fight as he has liberty issues. Those one-point-jump-away support stones are extremely useful in contact fights, and are commonly a reason to not adhere to the "crosscut? extend!" proverb because of their added value. If White instead chooses to pull back:
- Click Here To Show Diagram Code
[go]$$Bcm16 Establishing a base
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . 3 5 . O . . . . . . . . . O O . . |
$$ | . . 2 X . . . 1 . , . . . O . X . . . |
$$ | . . 4 . . X . . . . . . . . . . X . . |
$$ | . . . . . . . . . . . . . . . X O . . |
$$ | . . b . . . . . . . . . . . . O X . . |
$$ | . . 6 a . . . . . . . . . . . . X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . B . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . O . . . . . . . . . . . . X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . X . O . . . , . . . . . X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]
I can establish a base on the left, and Black has the marked weak stone to aim at as well. Not only this, but there is still plenty of aji in the White stone at the top. I would prefer to play

at "a", but I think Black responding with "b" is too severe. Again, the value of the marked stone shows itself as it prevents Black from descending to deprive White of eyespace on the edge:
- Click Here To Show Diagram Code
[go]$$Bcm16 Descent is messy
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . 8 9 . . . . . . . . . . . . . . |
$$ | . 5 3 6 7 O . . . . . . . . . O O . . |
$$ | . . 2 X 0 . . 1 . , . . . O . X . . . |
$$ | . . 4 . . X . . . . . . . . . . X . . |
$$ | . . . . . . . . . . . . . . . X O . . |
$$ | . . . . . . . . . . . . . . . O X . . |
$$ | . . . . . . . . . . . . . . . . X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . X . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . O . . . . . . . . . . . . X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . X . O . . . , . . . . . X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]
So, I'm guessing Black will want the key shape / separation point:
- Click Here To Show Diagram Code
[go]$$Bcm16 Corner in sente
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . 0 . . . . . . . . . . . . . . . |
$$ | . . 4 3 . O . . . a . . . . . O O . . |
$$ | . . 2 X . . . 1 . , . . . O . X . . . |
$$ | . 6 5 . . X . . . . . . . . . . X . . |
$$ | . 8 7 . . . . . . . . . . . . X O . . |
$$ | . . 9 . . . . . . . . . . . . O X . . |
$$ | . . . . . . . . . . . . . . . . X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . X . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . O . . . . . . . . . . . . X . . |
$$ | . . . . . b . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . X . O . . . , . . . . . X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]
Now however, White gets to take the corner, is likely to keep sente (hugely important right now) and retain much of the aji at "a" for later. If this plays out, I intend on playing "b" at the end of the sequence. It's hard for Black to develop the lower side because the 3-3 is open for invasion in the bottom right still. So, this feels unfavourable for Black too. Because this move seems to maximise my options and maintain my focus on the upper part of the left side (an area I think is the most urgent right now), I've gone with it
