What are properties of the STRIPS planning formalism in comparison to the other four formalisms?

It is a relatively simple formalism

It is a relatively difficult formalism

It is one of the most powerful formalisms

It is equally powerful as some formalisms

It is one of the least powerful formalisms

Consider the STRIPS planning task $\Pi = \langle V, I, G, A\rangle$ with binary variables $V = \{a,b,c,d,e\}$, initial state $I = \{a,c\}$, goal $G = \{a,e\}$, and operators $A = \{a_1,a_2,a_3,a_4\}$, where

• $\mathit{pre}(a_1) = \{a,c\}$, $\mathit{add}(a_1) = \{b\}$, $\mathit{del}(a_1) = \{a,c\}$, $\mathit{cost}(a_1) = 2$
  
• $\mathit{pre}(a_2) = \{c\}$, $\mathit{add}(a_2) = \{a,d\}$, $\mathit{del}(a_2) = \{\}$, $\mathit{cost}(a_2) = 4$
  
• $\mathit{pre}(a_3) = \{b\}$, $\mathit{add}(a_3) = \{a,e\}$, $\mathit{del}(a_3) = \{\}$, $\mathit{cost}(a_3) = 5$
  
• $\mathit{pre}(a_4) = \{d\}$, $\mathit{add}(a_4) = \{e\}$, $\mathit{del}(a_4) = \{c\}$, $\mathit{cost}(a_4) = 4$

What is the cost of an optimal plan for $\Pi$?