(* data: remove the markings *)
val data : 'a marked -> 'a
+ val kane : 'a marked -> 'a
(* ext: retrieve positional information from marked value*)
val ext : 'a marked -> ext option
fun naked d = (d, NONE)
fun data (d, e) = d
+ val kane = data
fun ext (d, e) = e
fun extmin ((l1, c1), (l2, c2)) =