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

The annoying case is (Z/p^2Z)^2 with H=pG; the paper proves bounds on transversal difference sets and conjectures the exact value.

Survey of structured lattices, mostly well-rounded ones, with the usual detour into post-quantum crypto and secure wireless.