let cmp_out_key k1 k2 = match k1, k2 with | OutRet, OutRet -> 0 | OutRet, (OutLoc _) -> -1 | (OutLoc _), OutRet -> 1 | OutLoc l1, OutLoc l2 when Locations.Zone.equal l1 l2 -> 0 | OutLoc _, OutLoc _ -> raise Not_equal