In Artificial Intelligence (AI), what is present in the planning graph ?

Answer: a sequence of levels (a planning graph).

Explanation: A planning graph is a leveled (layered) structure that alternates between proposition (literal) levels and action levels. It records which literals and actions are possible at each level and also records mutual-exclusion (mutex) relations.

• Proposition (literal) levels: contain the set of literals that may hold at that level.

• Action levels: contain actions whose preconditions are present in the preceding proposition level.

• Mutex relations: capture incompatibilities between pairs of literals or pairs of actions at the same level.

• Uses: detect when goals become reachable, determine graph leveling, and derive heuristics such as relaxed plan length.

Why the other answer choices are not fully correct:

• Literals: present in the graph but only one component; the graph also includes action levels and mutexes.

• Variables: planning graphs work with propositions/literals and actions rather than a separate variable-level structure.

• Heuristic estimates: are computed from the planning graph but are not themselves elements stored inside the graph.