Cofactor Explained: Clearing Elliptic Curves' dirty little secret
It's sad that efficient complete formulas for Weierstrass curves were found only after Curve25519 was well established. Now we are stuck with all these cofactor issues. Ristretto is nice but so terribly complex: <a href="https://ristretto.group/details/isogenies.html" rel="nofollow">https://ristretto.group/details/isogenies.html</a>