Rene: Dear, as said: P2, Q2, R2, S3 should already lead to an error, but it does only AFTER a further move. but the 4 moves all got accepted; hence, I was believed to be on the right track initially.
Suggestion to update L200 to indicate an incorrect move sooner (as for all the other levels).
caranthir: I understood what you meant. Still, it has educational value to show also refuting moves in problems. If any incorrect move immediately ends a problem every time, one does not get to see any refuting moves that demonstrate why the line chosen was bad. What you are asking is contradictory to the preferences of the majority of users, as far as I know: usually people ask us to add in "incorrect", i.e. refuting variations, not to remove them (actually, you are the first one of the latter kind that I have seen). Btw, the existence of refuting variations does not make any difference if one is solving problems in the most rigorous fashion, that is, by reading alone and not by trial and error.
Rene: Solved it but there's an error.. it accepts P2, Q2, R2 and S3, and then no matter what you do you receive an error.. seriously no learning curve here.
Eventually, I played P2 followed by R2 (again). This time no error, and easy solution.
caranthir: The moves you played to solve the problem (if you received that message) are the only moves that work; namely, P2, then if opponent answers with Q1, we immediately play R2, then R1, S1, T1, Q2, S1, S3, T3, T2, as per the way the opponent is made to resist here. Speaking of sequences that don't work, I don't see any errors in opponent's refutation moves. That is, no move works that shouldn't work, and if it says "error", there is no possible way to continue, and either your last move *or already some earlier move* was a mistake. --- This problem is considerably harder than others in this collection. It might be helpful to look at it with real stones and board if you have those, or with an sgf editor.
aponty: To be fair to the people having trouble with this problem, it is something like a 15kyu-10kyu-ish problem in a 25kyu problem set. I think that makes it a great final problem for the set though!
This shouldn't be 2k...