private GVCongruenceClass createCongruenceClass(Object label){
  int index=B.size();
  GVCongruenceClass result=new GVCongruenceClass(index,label);
  B.add(result);
  return result;
}

private GVCongruenceClass createCongruenceClass ( Object label ) { int index = B . size ( ) ; GVCongruenceClass result = new GVCongruenceClass ( index , label ) ; B . add ( result ) ; return result ; }
given a label , return a new congruence class for that label .
