return obj != null && removeFromColumnIf(Maps.valuePredicateOnEntries(equalTo(obj)));
      }

      @Override
      public boolean removeAll(Collection<?> c) {
        return removeFromColumnIf(Maps.valuePredicateOnEntries(in(c)));
      }

      @Override
      public boolean retainAll(Collection<?> c) {
        return removeFromColumnIf(Maps.valuePredicateOnEntries(not(in(c))));
      }