Recently I am working on monero source code, and I wonder how monero verify ed25519 public key is invalid. Is this function converting the public key into Y coordinates, then calculating the X coordinates, and verifying whether the coordinate points are on the elliptic curve? I was confused about the converting process. And also, does any Y coordinates have a corresponding X coordinates? Why this verify process will be failed if public key is invalid? Thanks so much! ge_frombytes_vartime is here.