Primary author-hosted manuscript: sites.lsa.umich.edu/idolga-new/wp-content/uploads/sites/1467/2024/08/hesse09.pdf
Publisher: ems.press/journals/lem/articles/12146
Section 2, manuscript pp.3–5: Hesse equations, common flex/base points, normal form and Hessians. Published in L’Enseignement Mathématique 55 (2009), pp.235–273. The wiki calculations explicitly use complex coefficients to avoid small-characteristic Hessian degeneracies.