I belive to have found a typo in an example in the Scala spec. More specifically, referring to the document on github (07-implicits.md), the call (line 158)
sort(yss)(xs: List[Int] => list2ordered[Int](xs)(int2ordered))
should probably read
sort(yss)((xs: List[Int]) => list2ordered[Int](xs)(int2ordered))
because the single parameter has the type specified.