Complete inequality description of the Hamiltonian cycle polytope

Determine the complete set of linear inequalities defining the symmetric traveling salesman polytope (Hamiltonian cycle polytope) of the complete graph $K_n$.

Background

The paper distinguishes the symmetric traveling salesman polytope PSTSP,nP_{\mathrm{STSP},n}, defined as the convex hull of incidence vectors of Hamiltonian cycles of KnK_n, from the subtour elimination (Held--Karp) relaxation polytope PSEP,nP_{\mathrm{SEP},n}. Although the latter has a standard tractable description by degree and subtour inequalities, it is generally a strict relaxation of the Hamiltonian cycle polytope. A complete inequality description of PSTSP,nP_{\mathrm{STSP},n} would characterize exactly which edge-weight vectors lie in the convex hull of Hamiltonian cycles, rather than merely in the Held--Karp relaxation.

References

The complete set of inequalities defining $P_{\mathrm{STSP},n}$ is not known, in general .

— Polytopes of Effective Boundary Expressions of Divisors on $\overline{M}_{0,n}$  (2608.18533 - Cavey et al., 19 Aug 2026) in Section 2, subsection 'Hamiltonian cycle and Held--Karp relaxation polytopes'