private boolean isExtra(Variable v) {
    return v != null && extras != null && extras.contains(v);
  }
private boolean isExtra(Variable v) {
    return v != null && extras != null && extras.contains(v);
  }
private boolean isExtra ( Variable v ) { return v != null && extras != null && extras . contains ( v ) ; }
Has v already been added to the set of extra variables?
Has v already been added to the set of extra variables?