Takeback and mate

White takes back his last move and mates in 1 instead
a) diagram
b) move bNh3 to c3, then solve again

a) Retract Ne7xRc6, Play Nd5#
b) Retract Re5xNe8 (not Re5xBe8!), play Bg5#

seems correct 😉

Originally posted by David113
a) Retract Ne7xRc6, Play Nd5#
b) Retract Re5xNe8 (not Re5xBe8!), play Bg5#

Correct. In b), Re5xBe8?? is illegal, because the Bishop never could have reached e8 in the first place (Pd7 and f7 have not moved).

Originally posted by David113
a) Retract Ne7xRc6, Play Nd5#
b) Retract Re5xNe8 (not Re5xBe8!), play Bg5#

After the Bg5 move,
Bg5+? Nxg5

Originally posted by Alethia
After the Bg5 move,
Bg5+? Nxg5

But the N is on c3 in part b), not h3.

Originally posted by BigDoggProblem
But the N is on c3 in part b), not h3.

Oh right. Thanks, I knew I had something worng, but I didn't do it on
a board.
😳

Originally posted by David113
a) Retract Ne7xRc6, Play Nd5#
b) Retract Re5xNe8 (not Re5xBe8!), play Bg5#

b) can also be solved by taking back Rg8xe8 (a knight).

Originally posted by Gastel
b) can also be solved by taking back Rg8xe8 (a knight).

The R needs to stay on the e-file to guard Be4.