Halim Djerroud

DEPTH (DEL Epistemic Planner with Tier Heuristics) is our entry to the first Epistemic Planning Track of the International Planning Competition 2026. Built in C++17 on top of the plank toolkit and packaged as an Apptainer container, it supports EPDDL specifications across the basic, intermediate, and hard levels. The core algorithm, Epistemic H*, is a two-queue best-first search adapted to Dynamic Epistemic Logic (DEL) — a transposition to the epistemic setting of the H* motion planner originally introduced for Navigation Among Movable Obstacles. A primary queue (OPEN) advances toward the goal by prioritising successors that strictly improve a coarse but informative tier heuristic, while a secondary queue (INCONS) retains setup actions (announcements, sensing steps, signal-passing) whose effect is invisible to the heuristic but enables later goal-achieving actions; when OPEN is empty, INCONS is flushed back into it, ensuring completeness despite the inadmissible heuristic. Bisimulation contraction is applied to every successor, so logically indistinguishable states are identified regardless of how they were reached. Epistemic H* is proven complete for finite DEL planning tasks. On the IPC 2026 sample benchmarks, DEPTH solves Grapevine (32 worlds) in milliseconds where the reference BFS planner exhausts the 60-second timeout.