code: public <C,R> NarrowedFlatMap<C,R> concreteFlatMap(Kleisli<W,C,R> widen){
          return new NarrowedFlatMap<>(widen);
      }
docs: Use concreteFlatMap to access a flatMap operator that works with the concrete type (rather than the higher kind encoding)
  
  e.g. using a vavr Vector
  
  <pre>
  {@code
  Active<vector,Integer> vector = Vectors.allTypeclasses(Vector.of(1,2,3));
  
  vector.concreteFlatMap(Vectors.kindKleisli())
  .flatMap(i->Vector.of(1,2,3)); //flatMap accepts Vector rather than Higher<vector,T>
  
  }
  </pre>
  
  Note this is not typically needed for cyclops-react types