New proof settles A(4)=4 for a 2-group problem via a single-vector argument

A researcher's open notebook on Kakeya-type problems reports a result on finite 2-groups whose involutions are all central. The author applies a closer look at a single vector to sharpen a restriction lemma from an earlier post. The analysis establishes that the invariant A(4) equals 4, which settles the question for groups with a self-centralising normal subgroup of the form Z_4^a x Z_2^b. The argument relies on anisotropic linear systems and a polar form, and it also establishes M(4)=4. The author notes that part of the verification was computer-assisted and that the associated tests passed before publication.