Question 3:

This question is about semantic 
checking in the context of a planning application. 
Such plans are successfully solved by
translating the plans to CSP instances
(but here we are not concerned with the translation).
The structure of a plan is given by the class dictionary
called Plans. A plan consists of objects, predicates and
operators.

The objects part defines the objects that may be used elsewhere
in the plan.
The predicates part defines the predicate namess that may be used elsewhere
in the plan.
The operators part defines the operator names
that may be used elsewhere
in the plan and it gives the definies of the operators in terms
of preconditions and effects.

The class dictionary, program and input and output are given
below. Find the UNKNOWNs.
UNKNOWN1 to UNKNOWN4  are titles that get printed.
They have a special status and must be derived
from understanding the semantic checking problem. Each
appears twice in the text.
The titles must succinctly describe the nature of the output
that follows.
UNKNOWN5 is a short piece of program text.


// class dictionary Plans

import edu.neu.ccs.demeter.dj.*;
import java.util.*;

Plans = Set(Plan).
Plan = "objects" <objects> Set(Obj) 
  "predicates" <predicates> Set(PredName) 
  "operators" <operators> Set(Op) 
  "initial" <initial> Set(PosLit) 
  "goal" <goal> Set(Literal)
  "solution" Set(OpName).
Literal : PosLit | NegLit common PredName <args> Set(Obj).
PosLit = .
NegLit = "!".
Op = OpName "preconditions" <preconditions> Set(Literal) 
            "effects" <effects> Set(Literal).

Obj = Ident.
PredName = Ident.
OpName = Ident.

Set(S) ~ "(" {S} ")".
Main = .


PROGRAM
-------------------------------------------------------------------

Main {
  public static void main(String args[]) throws Exception {{
    Plans m = Plans.parse(System.in);
    ClassGraph cg1 = new ClassGraph(true, false);
    final ClassGraph cg = new ClassGraph(cg1,
        "from Plans bypassing -> *,tail,* to *");
    cg.traverse(m, "from Plans to Plan", new Visitor(){
      void before(Plan host) {
        host.process(cg); }
      });

    System.out.println("done");
  }}
}
Plan {
{{
  void process(ClassGraph cg){
    System.out.println(" UNKNOWN1 ");
    cg.traverse(this
    ,"from Plan via ->*,objects,* to Obj", new Visitor(){
      void before (Obj host) {System.out.println(host.get_ident());}
      });
    System.out.println(" UNKNOWN2 ");
    cg.traverse(this
    ,"from Plan bypassing ->*,objects,* to Obj", new Visitor(){
      void before (Obj host) {System.out.println(host.get_ident());}
      });
    System.out.println(" UNKNOWN3 ");
    cg.traverse(this
    ,"from Plan via ->*,predicates,* to PredName", new Visitor(){
      void before (PredName host) {System.out.println(host.get_ident());}
      });
    System.out.println(" UNKNOWN4 ");
    cg.traverse(this
    ,"from Plan bypassing ->*,predicates,* to PredName", new Visitor(){
      void before (PredName host) {System.out.println(host.get_ident());}
      });
    System.out.println("The number of operators defined by the plan ");
    UNKNOWN5;
  }
}}
}

INPUT
-------------------------------------------------------------

(
objects (Battery1 Battery2 Cap Flashlight)
predicates (On In)
operators (
  PlaceCap 
  preconditions (!On(Cap Flashlight))
  effects (On(Cap Flashlight))
  RemoveCap 
  preconditions (On(Cap Flashlight))
  effects (!On(Cap Flashlight))
  Insert1
  preconditions (!On(Cap Flashlight) !In(Battery1 Flashlight))
  effects (In(Battery1 Flashlight))
  Insert2
  preconditions (!On(Cap Flashlight) !In(Battery2 Flashlight))
  effects (In(Battery2 Flashlight))
  )
initial (On(Cap Flashlight))
goal ( 
       On(Cap Flashlight) 
       In(Battery1 Flashlight)
       In(Battery2 Flashlight)
     )
solution(RemoveCap Insert1 Insert2 PlaceCap)
)

OUTPUT
-------------------------------------------------------------


 UNKNOWN1 
UNKNOWN6
UNKNOWN7
UNKNOWN8
UNKNOWN9
 UNKNOWN2 
Cap
Flashlight
Cap
Flashlight
Cap
Flashlight
Cap
Flashlight
Cap
Flashlight
Battery1
Flashlight
Battery1
Flashlight
Cap
Flashlight
Battery2
Flashlight
Battery2
Flashlight
Cap
Flashlight
Cap
Flashlight
Battery1
Flashlight
Battery2
Flashlight
 UNKNOWN3 
UNKNOWN10
UNKNOWN11
 UNKNOWN4 
On
On
On
On
On
In
In
On
In
In
On
On
In
In
The number of operators defined by the plan 
4
done