Explicit Involution Geometry of Product Kummer Surfaces

Revised review with full fixed-locus and cohomology calculations for the standard affine two-torsion subgroup of a product Kummer surface. Classical Lieberman constructions are credited; this is not a classification of all K3 or Enriques involutions. We classify the 31 nonidentity involutions in the standard affine two-torsion subgroup of a product Kummer surface. We compute their fixed loci, quotient surfaces and rational cohomology representations, including the fixed loci of all fifteen translations descending to each of the nine Lieberman quotients.