MAYBE
* Step 1: Failure MAYBE
  + Considered Problem:
      - Strict TRS:
          #less(@x,@y) -> #cklt(#compare(@x,@y))
          append(@l1,@l2) -> append#1(@l1,@l2)
          append#1(::(@x,@xs),@l2) -> ::(@x,append(@xs,@l2))
          append#1(nil(),@l2) -> @l2
          flatten(@t) -> flatten#1(@t)
          flatten#1(leaf()) -> nil()
          flatten#1(node(@l,@t1,@t2)) -> append(@l,append(flatten(@t1),flatten(@t2)))
          flattensort(@t) -> insertionsort(flatten(@t))
          insert(@x,@l) -> insert#1(@l,@x)
          insert#1(::(@y,@ys),@x) -> insert#2(#less(@y,@x),@x,@y,@ys)
          insert#1(nil(),@x) -> ::(@x,nil())
          insert#2(#false(),@x,@y,@ys) -> ::(@x,::(@y,@ys))
          insert#2(#true(),@x,@y,@ys) -> ::(@y,insert(@x,@ys))
          insertionsort(@l) -> insertionsort#1(@l)
          insertionsort#1(::(@x,@xs)) -> insert(@x,insertionsort(@xs))
          insertionsort#1(nil()) -> nil()
      - Weak TRS:
          #cklt(#EQ()) -> #false()
          #cklt(#GT()) -> #false()
          #cklt(#LT()) -> #true()
          #compare(#0(),#0()) -> #EQ()
          #compare(#0(),#neg(@y)) -> #GT()
          #compare(#0(),#pos(@y)) -> #LT()
          #compare(#0(),#s(@y)) -> #LT()
          #compare(#neg(@x),#0()) -> #LT()
          #compare(#neg(@x),#neg(@y)) -> #compare(@y,@x)
          #compare(#neg(@x),#pos(@y)) -> #LT()
          #compare(#pos(@x),#0()) -> #GT()
          #compare(#pos(@x),#neg(@y)) -> #GT()
          #compare(#pos(@x),#pos(@y)) -> #compare(@x,@y)
          #compare(#s(@x),#0()) -> #GT()
          #compare(#s(@x),#s(@y)) -> #compare(@x,@y)
      - Signature:
          {#cklt/1,#compare/2,#less/2,append/2,append#1/2,flatten/1,flatten#1/1,flattensort/1,insert/2,insert#1/2
          ,insert#2/4,insertionsort/1,insertionsort#1/1} / {#0/0,#EQ/0,#GT/0,#LT/0,#false/0,#neg/1,#pos/1,#s/1,#true/0
          ,::/2,leaf/0,nil/0,node/3}
      - Obligation:
          innermost runtime complexity wrt. defined symbols {#cklt,#compare,#less,append,append#1,flatten,flatten#1
          ,flattensort,insert,insert#1,insert#2,insertionsort,insertionsort#1} and constructors {#0,#EQ,#GT,#LT,#false
          ,#neg,#pos,#s,#true,::,leaf,nil,node}
  + Applied Processor:
      Ara {heuristics_ = NoHeuristics, minDegree = 1, maxDegree = 3, araTimeout = 60, araFindStrictRules = Nothing, araSmtSolver = MiniSMT}
  + Details:
      The input can not be schown compatible.
MAYBE