MAYBE
TRS:
 {          is_empty(nil()) -> true(),
       is_empty(cons(x, l)) -> false(),
             hd(cons(x, l)) -> x,
             tl(cons(x, l)) -> l,
   ifappend(l1, l2, true()) -> l2,
  ifappend(l1, l2, false()) -> cons(hd(l1), append(tl(l1), l2)),
             append(l1, l2) -> ifappend(l1, l2, is_empty(l1))}
 DP:
  Strict:
   {ifappend#(l1, l2, false()) -> hd#(l1),
    ifappend#(l1, l2, false()) -> tl#(l1),
    ifappend#(l1, l2, false()) -> append#(tl(l1), l2),
               append#(l1, l2) -> is_empty#(l1),
               append#(l1, l2) -> ifappend#(l1, l2, is_empty(l1))}
  Weak:
  {          is_empty(nil()) -> true(),
        is_empty(cons(x, l)) -> false(),
              hd(cons(x, l)) -> x,
              tl(cons(x, l)) -> l,
    ifappend(l1, l2, true()) -> l2,
   ifappend(l1, l2, false()) -> cons(hd(l1), append(tl(l1), l2)),
              append(l1, l2) -> ifappend(l1, l2, is_empty(l1))}
  EDG:
   {(append#(l1, l2) -> ifappend#(l1, l2, is_empty(l1)), ifappend#(l1, l2, false()) -> append#(tl(l1), l2))
    (append#(l1, l2) -> ifappend#(l1, l2, is_empty(l1)), ifappend#(l1, l2, false()) -> tl#(l1))
    (append#(l1, l2) -> ifappend#(l1, l2, is_empty(l1)), ifappend#(l1, l2, false()) -> hd#(l1))
    (ifappend#(l1, l2, false()) -> append#(tl(l1), l2), append#(l1, l2) -> is_empty#(l1))
    (ifappend#(l1, l2, false()) -> append#(tl(l1), l2), append#(l1, l2) -> ifappend#(l1, l2, is_empty(l1)))}
   SCCS:
    Scc:
     {ifappend#(l1, l2, false()) -> append#(tl(l1), l2),
                 append#(l1, l2) -> ifappend#(l1, l2, is_empty(l1))}
    SCC:
     Strict:
      {ifappend#(l1, l2, false()) -> append#(tl(l1), l2),
                  append#(l1, l2) -> ifappend#(l1, l2, is_empty(l1))}
     Weak:
     {          is_empty(nil()) -> true(),
           is_empty(cons(x, l)) -> false(),
                 hd(cons(x, l)) -> x,
                 tl(cons(x, l)) -> l,
       ifappend(l1, l2, true()) -> l2,
      ifappend(l1, l2, false()) -> cons(hd(l1), append(tl(l1), l2)),
                 append(l1, l2) -> ifappend(l1, l2, is_empty(l1))}
     Fail