Special vertices in the Grünbaum–Shephard–Geis catalogue

Determine which irreducible simplicial arrangements in the Grünbaum–Shephard–Geis catalogue of arrangements in real projective three-space admit a special vertex.

Background

The paper establishes that the irreducible crystallographic Coxeter arrangements of types A4 and B4 admit a special vertex, while those of types D4 and F4 do not. It also exhibits a deletion chain of irreducible simplicial arrangements inside B4 with this property.

The authors then ask for a classification across the broader Grünbaum–Shephard–Geis catalogue. Resolving this question would determine how widespread the special-vertex property is among known irreducible simplicial arrangements in projective three-space.

References

Question 7.7. Which irreducible simplicial arrangements in the Gr¨unbaum–Shephard–Geis catalogue [5, 4] admit a special vertex ?

Simplicial arrangements in real projective three-space revisited  (2608.28254 - Janasz et al., 28 Aug 2026) in Question 7.7, end of Section 7