scala> val l = Set(Right(1), Left("a"), Right(3), Left("b"))
l: scala.collection.immutable.Set[Product with Serializable with Either[java.lang.String,Int]] = Set(Right(1), Left(a), Right(3), Left(b))

scala> for (e <- l; n <- e.right) yield n
<console>:9: error: type mismatch;
 found   : Product with Either[java.lang.String,Int] with Serializable
 required: scala.collection.GenTraversableOnce[?]
              for (e <- l; n <- e.right) yield n