The classical Kummer construction attaches a K3 surface to an abelian surface. As Shioda and Katsura showed, this construction breaks down for supersingular abelian surfaces in characteristic two. Replacing supersingular abelian surfaces by the self-product of the rational cuspidal curve, and the sign involution by suitable infinitesimal group scheme actions, we give the correct Kummer-type construction for this situation. We encounter rational double points of type D 4 and D 8 instead of type A 1 . It turns out that the resulting surfaces are supersingular K3 surfaces with Artin invariant one and two. They lie in a 1-dimensional family obtained by simultaneous resolution, which exists after purely inseparable base change.
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STEFAN SCHRÖERmaterial on blowing up rational surface singularities along curves. We use this in Section 11, where we consider blowing ups of Weil divisors in genus-one fibrations. This is crucial in Section 12, where we view our normal K3 surfaces as lying in a family Z → S, and show that this family admits a simultaneous resolution X → S after a purely inseparable base change S → S. In the last section we show that this family is induced from a family X → P 1 .