Duality closure of Mandel oriented matroids

Determine whether the class of Mandel oriented matroids is closed under duality.

Background

Mandel oriented matroids are defined through the existence of a general-position extension whose associated oriented matroid programs are all Euclidean. The paper proves minor-closure under contractions and deletions that do not reduce rank, and proves broader minor-closure results in low-rank and uniform cases, but does not settle duality closure. The dual of R(20) is Las Vergnas, yet its Mandel status is unknown.