question.txt

Implement the standard algorithm for CTL model checking on Kripke structures. 
You may use any programming language(s) that you prefer, without compromising the efficiency. 


Input : 
 A kripke structure K and a CTL formula $\phi$.  
 
For simplicity of parsing, you may assume that the formula is fully parenthesized.
 Assume that the set of atomic propositions are p1, p2, .... 
 You may consider K as a directed graph (with states as vertices and transitions as edges) with a labelling function that associates 
 a subset of atomic propositions with each state. 
 
Step 1 : Convert the formula $\phi$ into an equivalent formula $\psi$ in which a conveninent minimal set of CTL operators only are used. 
        a) Output the resultant formula $\psi$ (mention which is the minimal set that you are choosing). 
        b) Output the number of nodes (including leaves) in the parse tree of $\psi$.
        c) In the bottom-up order, for each node of the parse-tree, output the node-id and 
          subformula corresponding to that node. 
        d) Store the parse tree of $\psi$ for later processing. 
         
Step 2 : Implement the bottom-up CTL model checking algorithm that outputs the subset of states of K that satisfies $\psi$. 
Choose an appropriate data structure so that looking up the set of states that satisfy the formula(s) corresponding to the immediate subtrees of
a node in the parse tree can be quickly done and the additional computation at a node is also efficiently done.
Make sure that the time spent per node of the parse tree is at most quadratic (preferably linear) in the size of K. 
After processing each parse-tree node, output its node-id and the subset of states of K that satisfy the subformula corresponding to that node.