Incorrect exercise kbjBT

lishogi.org/training/kbjBT

In this problem after 1.N’33 2.Px, there are 2 moves that lead to checkmate on move 7:

3.S’32 4.K51 5.R’41 6.K62 7.R71+, checkmate, which is the accepted answer

And

3.R61 4.G’51 5.S’32 6.K42 7.S31+, checkmate, which is not accepted

Either both solutions should be accepted or the problem should be removed...

After 6. K-42, you are correct that it is a mate.
The second line is not accepted because 6. K-52 and there is no mate.

@LizardWizard
There is a White Gold on 52, so 6.K52 is not a move.

My line was after Gote drops on 51 on move 4.
If instead Gote moves backwards with 4.G51(52) , then 5.S’52 is an immediate checkmate.

Ok, actually the White S63 defends.

@Evargalo
Ah, I thought you meant 4. G(52)-51. That's not mate because then the king can indeed move to 52, like I said.
But Gote would not play 4. G*51 on move 4 either, that WOULD be mate. Playing G(52)-51 is the only defense.