Complete obstruction set of forbidden t‑minors for t‑perfection

Identify and characterize the complete set of forbidden t‑minors that precisely determine t‑perfection; that is, derive a full list of t‑minor obstructions such that a graph is t‑perfect if and only if it contains none of these t‑minors.

Background

The paper’s proofs rely only on odd wheels as forbidden t‑minors to bound the chromatic number, but the authors note that additional forbidden t‑minors (e.g., even Möbius ladders) are known to force t‑imperfection. A comprehensive forbidden t‑minor characterization would mirror the role that forbidden induced subgraphs play for perfect graphs and remains a central unresolved goal.