Can Richelot (2,2) isogenies be done without derivatives? This paper says yes, via subresultants and algebraic checks.

Models supersingular isogenies of 2^k and 3^k degree as zero-dimensional polynomial systems, then pokes Gröbner bases at them.

Computational PPAV framework, with theta-model algorithms for automorphism groups and higher-dimensional isogeny interpolation.