== empty ==
fun empty() {}
---------------------
l0:
    <START>        NEXT:[read (Unit)]    PREV:[]
    read (Unit)    NEXT:[<END>]          PREV:[<START>]
l1:
    <END>          NEXT:[<SINK>]         PREV:[read (Unit)]
error:
    <ERROR>        NEXT:[]               PREV:[]
sink:
    <SINK>         NEXT:[]               PREV:[<END>]
=====================