Problem #5281

[roq]

This one is sort of the converse to the previous problem I mentioned – i.e. white gets a material advantage, but the solution should not end there. You can see by the low rating and time taken that people are just snapping off the knight without calculating the consequences. But there is quite a subtle second move for white that one must see to avoid black winning by queening the b pawn. i.e. After 1. bxa4 b3 white must play 2. Ne7+!! – using the tempo gained by the check to reposition his knight so it can hold the b pawn. All other moves lose. If this second move was included in the solution it would be a really great problem.


Perhaps you might include another rule i.e:

-   A move is forcing if it is some fixed evaluation amount (say a pawn) better than all other moves.
-   If a move is followed by a forcing move on the next move then the solution line should continue until there are no more forcing moves.         

P.S.1 I just wanted to mention again that suspect problems are actually quite uncommon (no more than 1 in 10 I’d estimate - Many of the problems given low stars elsewhere look quite OK to me). Its just that I’ve being doing a lot of problems recently. Many of the problems are excellent and I’ve marked them with four or five stars. So to some extent this is all gilding the lily.

P.S.2 I noticed a few aggrieved comments about alternative three move mates not being allowed when the solution is a two move mate – so maybe the rule of requiring two move mates to be exact might be a bit strict.     

[richard]

Hi Roq,

It would certainly be nice to have the tactic include the apsects around the threat of promotion.  Unfortunately one of the weaknesses of the current generator is that it doesn't handle problems involving pawns very well.  To avoid tactics finishing with pawn takes unrelated to the main tactic most parts of the code make a decision that pawn takes are non-interesting.

There is already a rule very similar to your proposed one in the system except that the fixed evaluation amount is larger than a pawn (and it is based on the value of threatened pieces rather than evaluations), without this many non-mating sequences would require the user to find pawn takes after the main point of the tactic is over which is probably not desirable.  There are other things which can override the forcing rule such as the situation where there are forcing moves but the material taken by both sides ends up being equal from that point on, so the sequence is halted.

Unfortunately I think I'm going to have to leave problems like this in the too hard basket for now,  at least until I've exhausted some of the lower hanging fruit around the mate problems.

Regards,
Richard.

[roq]

This is all really interesting. I think though that tempting as it is, I’m very much in danger of trying to teach my grandmother how to suck eggs (if I haven’t done so already). In any case you seem to have your hands full of eggs already (to mix metaphors a little).

[richard]

:-)

There are still a lot of different shaped eggs I don't understand yet, so your ideas are very welcome. You've already mentioned a few ideas worth pursuing.

Regards,
Richard.