#graphplan

Question 1: Single choice

In a GraphPlan planning graph, level 0 holds the initial facts, including (in R2 C). Two level-1 actions are (move-left R2 C B) (precondition (in R2 C); effects (in R2 B), delete (in R2 C)) and (carry-left R2 B1 C B) (preconditions (in R2 C), (in B1 C); effects (in R2 B), (in B1 B), delete (in R2 C), delete (in B1 C)). Why are these two actions mutex?

One adds (in R2 B) while the other deletes it (inconsistent effects)1
They are not mutex, because both can be done by robot R2 at once2
Each deletes (in R2 C), a precondition of the other (interference)3
Their preconditions are mutex at level 0 (competing needs)4

Timed test