EquationSystem {
{{
  static ClassGraph cg = new ClassGraph(true, false);
  static String usedVarsSpec =
    "from EquationSystem via -> *,rhs,* to Variable";
  static String definedVarsSpec =
    "from EquationSystem via -> *,lhs,* to Variable";
  HashSet collectVars(String travspec){
    Visitor v = new Visitor(){
      HashSet return_val = new HashSet();
      void before(Variable v1) {return_val.add(v1);}
      public Object getReturnValue(){return return_val;}
    };
    return (HashSet) cg.traverse(this, travspec, v);
  }
  HashSet getUsedVars() {
    return this.collectVars(usedVarsSpec);
  }
  HashSet getDefinedVars() {
    return this.collectVars(definedVarsSpec);
  }
}}
}