code: public static <T> Reducer<PersistentSet<T>,T> toPersistentSet() {
          return Reducer.fromMonoid(Monoids.concatPersistentCollection(HashSet.empty()), a -> HashSet.of(a));
      }
docs: <pre>
  {@code
  PersistentSet<Integer> q = Reducers.toPSet()
  .foldMap(Stream.of(1,2,3,4));
  
  }
  </pre>
  @return Reducer for PSet