code: public static <T,W> List<T> listFirst(List<Pair<T, W>> list) {
          ArrayList<T> ts = new ArrayList<T>();
          for (Pair<T, W> twPair : list) {
              ts.add(twPair.getFirst());
          }
          return ts;
      }
docs: Return a List of the first items from a list of pairs
  @param list list
  @param <T> first type
  @param <W> second type
  @return list of firsts