Untitled

Consider the following planning domain and problem:

Domain Facts: 
A(x),
B(x),
C,
D(x),
E(x,y)

Domain Actions (with parameters):
ACTION1 (x)
pre: A(x), B(x),C
eff: D(x), ¬ A(x), ¬B(x), ¬C(x)
ACTION2 (x)
pre: D(x)
eff: A(x), C, B(x), ¬D(x)
ACTION3 (x,y)
pre: A(y), D(x)
eff: C, A(x), E(x,y) ¬A(y), ¬D(x) 
ACTION4 (x,y)
pre: E(x, y), A(x), C
eff: D(x), A(y), ¬E(x,y), ¬A(x), ¬C

Initial State (with objects x1, x2)
B(x1), B(x2)
A(x1), A(x2)
C

Goal State (all facts to be satisfied): 
E(x1,x2)
Question: Using the Relaxed Planning Graph approach, how many action layers are required to enumerate all goal facts in a single fact layer? 

For this question, assume f(0) is our initial fact layer and a(1) is our first action layer. 

Question 12Answer

A.
0

B.
1

C.
It's not possible for all goal facts to appear in a single fact layer.

D.
3

E.
2