MAYBE
* Step 1: Failure MAYBE
  + Considered Problem:
      - Strict TRS:
          a() -> b()
          a() -> c()
          head(cons(x,xs)) -> x
          head(nil()) -> error()
          ifPlus(false(),x,y,z) -> plusIter(x,s(y),s(z))
          ifPlus(true(),x,y,z) -> y
          ifSum(false(),xs,x,y) -> sumIter(tail(xs),y)
          ifSum(true(),xs,x,y) -> x
          isempty(cons(x,xs)) -> false()
          isempty(nil()) -> true()
          le(0(),y) -> true()
          le(s(x),0()) -> false()
          le(s(x),s(y)) -> le(x,y)
          plus(x,y) -> plusIter(x,y,0())
          plusIter(x,y,z) -> ifPlus(le(x,z),x,y,z)
          sum(xs) -> sumIter(xs,0())
          sumIter(xs,x) -> ifSum(isempty(xs),xs,x,plus(x,head(xs)))
          tail(cons(x,xs)) -> xs
          tail(nil()) -> nil()
      - Signature:
          {a/0,head/1,ifPlus/4,ifSum/4,isempty/1,le/2,plus/2,plusIter/3,sum/1,sumIter/2,tail/1} / {0/0,b/0,c/0,cons/2
          ,error/0,false/0,nil/0,s/1,true/0}
      - Obligation:
          innermost runtime complexity wrt. defined symbols {a,head,ifPlus,ifSum,isempty,le,plus,plusIter,sum,sumIter
          ,tail} and constructors {0,b,c,cons,error,false,nil,s,true}
  + Applied Processor:
      Ara {heuristics_ = NoHeuristics, minDegree = 1, maxDegree = 3, araTimeout = 60, araFindStrictRules = Nothing, araSmtSolver = Z3}
  + Details:
      The input can not be schown compatible.
MAYBE