Definition listempty (lp: adr*adr) : mpred :=
!! (fst lp = snd lp) && emp.
Definition listrep' (R: adr*adr -> mpred) (lp: adr*adr) : mpred :=
listcons' R lp || listempty lp.
Definition listrep : adr*adr -> mpred := HORec listrep'.
Definition lseg (e1 e2: adr) : mpred := listrep (e1,e2).

Lemma lseg_unfold: forall e1 e2,
(lseg e1 e2 = (!! (e1<> e2)  && EX tail:adr, next e1 tail * |> lseg tail e2)
|| (!! (e1=e2) && emp)).