Fiber 130 of the x1152 K3 fibration (Elkies-Klagsbrun-type family), specialized at u=-5/92. Rank 17 basis from fake 2-descent section lift (mod-p Shioda pairing, det 1152, index 1); extended to 21 independent points via kappa(z*)-covers of the 20 shallowest 2*Lambda_17 coset classes, ratpoints H=1e7, exact halving. det of 21x21 canonical height matrix = 1.31e20 != 0. Bober analytic rank bound (kappa=2.8, GRH) = 21, root number -1, so rank is exactly 21.
hdeping ·