Puzzle Hints

1. See lemma 5.4.7 in the Zcash specs for Bob's reasoning on why to only use the x coordinate when storing the public keys

2. Note that the MNT curves are represented in Weierstrass from in the circuit, and use the fact that both (x,y) and (x,-y) are valid points for spending

3. Make sure you negate the y coordinate in the right scalar field, being the base field of MNT4

The winner of the puzzle write-up was submitted by niooss-ledger. You can view the solution and puzzle write-up here. The background material required to solve the puzzle is also covered in the write up.
There were many interesting write-up submissions which are linked below:
* Winning write-up by niooss-ledger
* Write-up by tjsharp1
* Write-up by sylvainpelissier
* Write-up by TrapdoorHeader
* Write-up by yannickseurin
* Write-up by rishotics
* Write-up by timgestson
* Write-up by 10to4
* Write-up by thor314
* Write-up by ndkoo
* Write-up by huy-tn
* Write-up by brozorec
* Write-up by dorebell
* Write-up by kkstar0