permutations.scala

@tailrec
             def permutations[T](alphabet: Set[T], s: Seq[Seq[T]] = Seq(Seq.empty[T])): Seq[Seq[T]] = 
               if(s.head.size == alphabet.size) s else {
                 val updatedSolutions = for {
                   partial <- s
                   chosen <- (alphabet -- partial)
                 } yield chosen +: partial
                 permutations(alphabet, updatedSolutions)
               }