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Existence of shellable but not CL-shellable finite atomic lattices

Determine whether there exist finite atomic lattices that are shellable but not CL-shellable; equivalently, ascertain whether an lcm-lattice of a monomial ideal can be shellable without being CL-shellable.

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Background

In general poset theory, CL-shellability implies shellability, but the converse fails: Vince and Wachs constructed a shellable poset that is not CL-shellable. However, their example is not a lattice. For lcm-lattices (equivalently, finite atomic lattices), no example is known that is shellable but not CL-shellable.

Clarifying whether such lattices exist would sharpen the relationship between shellability and CL-shellability in the specific context of lcm-lattices and could impact the understanding of the combinatorial-topological properties that correspond to algebraic properties of monomial ideals.

References

Another interesting question that arises is whether in the case of lcm-lattices (equivalently, finite atomic lattices), shellability is equivalent to CL-shellability. To our knowledge, there is no known example of a finite atomic lattice that is shellable but not CL-shellable. We thus pose the following question: Question 5.2. Do there exist finite atomic lattices that are shellable but not CL-shellable?

Linear quotients, linear resolutions and the lcm-lattice (2507.23520 - Varshavsky, 31 Jul 2025) in Section 5, Question 5.2