BQM 336

Difficulty: Intermediate   Keywords: Tactics, Problem
Black to play and capture white marked group

This is a capture problem and first variant was composed by Marcel Crasmaru and used in his Master Thesis to simplify Robson's proof that GO is EXP-time hard (see Complexity of Go), linked here from John Tromp logic rules page

I tried several variations, but all of them seem to fail. Am I overlooking something obvious, or is the problem composed wrongly?

Attempt 1 - direct

Direct attempt
Direct attempt (continued)

The direct attempt fails.

Attempt 2 - capture ko first

Second attempt: capture ko first
Second attempt (continued)

The second attempt - capturing the ko - fails as well, as the ladder cannot be avoided.

Comment from author

I overlooked this ladder; I should've put the stones on a larger board... -John

Attempt 3 - another failure

Third attempt: white escapes

As seems forced there is nothing to stop White from making eyes.

Attempt 4 - capturing race

blubb: Funnily, I came to the attempts above in exactly the same order (while temporarily ignoring yours). The problem somehow looks to me as if the ko capture should be the solution but the creator missed the alternative ladder (which works regardless of the ataried white stone). On the other hand, John is a careful thinker, so all in all ... no clue.

Fourth attempt: capturing race

Here's another idea - I can't quite see what it ends up like.

BQM 336 last edited by crasmarum on October 19, 2009 - 01:34