Attempt Number: 4
Error Message: Action not unique compared to other actions chosen from this state before. Choose a new action

Action Reasoning:
Board p4 onto fast1 at floor n2 because fast1 can hold one more passenger, and this aligns with the plan to eventually move p4 to floor n4.

New State Description:
- fast0: At floor n0, 0/2 passengers.- fast1: At floor n2, 2/2 passengers (p5 and p4 on board).- slow0-0: At floor n2, 0/1 passengers.- p0: On floor n2.- p1: On floor n1.- p2: On floor n5.- p3: On floor n5.- p4: On board fast1.- p5: On board fast1.- p6: On floor n2.

Action Chosen:
(board p4 fast1 n2 n1 n2)
