desugaring of a for comprehension for the herding-cats either example

nested-for.scala

//refers to http://eed3si9n.com/herding-cats/stacking-future-and-either.html

def isFriends1(user1: Long, user2: Long)
   (implicit ec: ExecutionContext): Future[Either[Error, Boolean]] =
   for {
     a <- followers(user1)
     b <- followers(user2)
   } yield for {
     x <- a.right
     y <- b.right
   } yield x.exists(_.id == user2) && y.exists(_.id == user1)

def isFriends1Desugared(user1: Long, user2: Long)
  (implicit ec: ExecutionContext): Future[Either[Error, Boolean]] =
  followers(user1).flatMap { a =>
    followers(user2).map { b =>
      a.right.flatMap { x =>
        b.right.map { y =>
          x.exists(_.id == user2) && y.exists(_.id == user1)
        }
      }
    }
  }