A convex body variant of Soberon's counterexample to the Grünbaum conjecture.
A Lean formalization of a geometric strengthening/variant of Pablo Soberón's counterexample to the Grünbaum four-hyperplane mass-partition conjecture. The formalized result constructs a convex body K in R^4 with nonempty interior such that no four affine hyperplanes divide K into sixteen sign cells of equal four-dimensional volume. Equivalently, the obstructed mass can be chosen to be uniform Lebesgue volume on a convex body. The proof adapts Soberón's explicit cubic/quartic tensor obstruction and replaces the smooth positive density used in the source by a small Wulff-body perturbation of…
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