The paper "Ordered Landmarks in Planning" by Jörg Hoffmann, Julie Porteous, and Laura Sebastia explores the concept of ordering constraints in planning tasks, extending previous work by Koehler and Hoffmann. The authors introduce the idea of "landmarks," which are facts that must be true at some point in every valid solution plan. They extend the notion of "reasonable orders" between top-level goals to include these landmarks and revise the definition to better capture the intuitive meaning of goal ordering. The paper presents methods for finding landmarks, approximating necessary orders between them, and using this information to decompose planning tasks into smaller sub-tasks. The methodology is domain- and planner-independent, and the authors demonstrate that their approach can significantly improve the runtime performance of state-of-the-art sub-optimal planning systems like FF and LPG. The paper includes detailed definitions, theoretical analyses, and empirical results across various domains.The paper "Ordered Landmarks in Planning" by Jörg Hoffmann, Julie Porteous, and Laura Sebastia explores the concept of ordering constraints in planning tasks, extending previous work by Koehler and Hoffmann. The authors introduce the idea of "landmarks," which are facts that must be true at some point in every valid solution plan. They extend the notion of "reasonable orders" between top-level goals to include these landmarks and revise the definition to better capture the intuitive meaning of goal ordering. The paper presents methods for finding landmarks, approximating necessary orders between them, and using this information to decompose planning tasks into smaller sub-tasks. The methodology is domain- and planner-independent, and the authors demonstrate that their approach can significantly improve the runtime performance of state-of-the-art sub-optimal planning systems like FF and LPG. The paper includes detailed definitions, theoretical analyses, and empirical results across various domains.