problem 46875

[boromir]

problem http://chesstempo.com/chess-problems/46875 is rather peculiar. The solution is mate in one. First alternative is mate in 7, which is not an alternative, but then as number 3 there's a mate in 9, which is marked as an alternative.
It doesn't really matter for the problem (you, quite reasonably, have to find the mate in 1 to solve it anyways), it's just a quite funny quirk of the problem generator.

[drahacikfm]

There are not supposed to be any alternates for mate in 1.  Richard said it's just a bug in the current generator which will be fixed next time.

[richard]

There are a couple of things going on with mate in 1's, firstly they should never have alternatives as Drahacik points out.  However there is a bug that is letting some in, things are further confused by the fact that longer mates are not usually allowed but the mate in 9 you see is probably being allowed as an alternative due to a material winning line during the mating sequence, not because it is a mate, this is why for example you can see a mate in 7 rejected as an alternative but a mate in 9 allowed.

Regards,
Richard.