#strips

Question 1: Single choice

In STRIPS, an action $a$ has a precondition set $pre(a)$ , an add set $add(a)$ and a delete set $del(a)$ . Backward state-space planning regresses a goal set $g$ through an action $a$ that is relevant to it. Which formula gives the regressed goal $g'$ ?

$g' = (g \setminus add(a)) \cup pre(a)$ 1
$g' = (g \setminus del(a)) \cup pre(a)$ 2
$g' = (g \setminus del(a)) \cup add(a)$ 3
$g' = (g \setminus add(a)) \cap pre(a)$ 4

Timed test