code: public Iterator<Tuple> getUsed( VarDef var, final boolean onceOnly)
      {
      return
        getBinds(
          IteratorUtils.filteredIterator(
            getUsed(),
            tuple -> tuple.isOnce() == onceOnly),
          var);
      }
docs: Returns input tuples already used in a test case that bind the given variable, considering
  only tuples that are (not) once-only