WORST_CASE(?,O(n^1))
* Step 1: Ara WORST_CASE(?,O(n^1))
    + Considered Problem:
        - Strict TRS:
            append(l1,l2) -> ifappend(l1,l2,l1)
            hd(cons(x,l)) -> x
            ifappend(l1,l2,cons(x,l)) -> cons(x,append(l,l2))
            ifappend(l1,l2,nil()) -> l2
            is_empty(cons(x,l)) -> false()
            is_empty(nil()) -> true()
            tl(cons(x,l)) -> l
        - Signature:
            {append/2,hd/1,ifappend/3,is_empty/1,tl/1} / {cons/2,false/0,nil/0,true/0}
        - Obligation:
            innermost runtime complexity wrt. defined symbols {append,hd,ifappend,is_empty,tl} and constructors {cons
            ,false,nil,true}
    + Applied Processor:
        Ara {heuristics_ = NoHeuristics, minDegree = 1, maxDegree = 3, araTimeout = 60, araFindStrictRules = Nothing, araSmtSolver = Z3}
    + Details:
        Signatures used:
        ----------------
          append :: [A(15) x A(15)] -(9)-> A(3)
          cons :: [A(5) x A(5)] -(5)-> A(5)
          cons :: [A(15) x A(15)] -(15)-> A(15)
          cons :: [A(9) x A(9)] -(9)-> A(9)
          cons :: [A(0) x A(0)] -(0)-> A(0)
          cons :: [A(3) x A(3)] -(3)-> A(3)
          false :: [] -(0)-> A(0)
          hd :: [A(5)] -(6)-> A(0)
          ifappend :: [A(0) x A(15) x A(15)] -(8)-> A(3)
          is_empty :: [A(9)] -(10)-> A(0)
          nil :: [] -(0)-> A(15)
          nil :: [] -(0)-> A(9)
          tl :: [A(0)] -(15)-> A(0)
          true :: [] -(0)-> A(0)
        
        
        Cost-free Signatures used:
        --------------------------
          append :: [A_cf(0) x A_cf(0)] -(0)-> A_cf(0)
          cons :: [A_cf(0) x A_cf(0)] -(0)-> A_cf(0)
          ifappend :: [A_cf(0) x A_cf(0) x A_cf(0)] -(0)-> A_cf(0)
          nil :: [] -(0)-> A_cf(0)
        
        
        Base Constructor Signatures used:
        ---------------------------------
          cons_A :: [A(1) x A(1)] -(1)-> A(1)
          false_A :: [] -(0)-> A(1)
          nil_A :: [] -(0)-> A(1)
          true_A :: [] -(0)-> A(1)
        
* Step 2: Open MAYBE
    - Strict TRS:
        append(l1,l2) -> ifappend(l1,l2,l1)
        hd(cons(x,l)) -> x
        ifappend(l1,l2,cons(x,l)) -> cons(x,append(l,l2))
        ifappend(l1,l2,nil()) -> l2
        is_empty(cons(x,l)) -> false()
        is_empty(nil()) -> true()
        tl(cons(x,l)) -> l
    - Signature:
        {append/2,hd/1,ifappend/3,is_empty/1,tl/1} / {cons/2,false/0,nil/0,true/0}
    - Obligation:
        innermost runtime complexity wrt. defined symbols {append,hd,ifappend,is_empty,tl} and constructors {cons
        ,false,nil,true}
Following problems could not be solved:
  - Strict TRS:
      append(l1,l2) -> ifappend(l1,l2,l1)
      hd(cons(x,l)) -> x
      ifappend(l1,l2,cons(x,l)) -> cons(x,append(l,l2))
      ifappend(l1,l2,nil()) -> l2
      is_empty(cons(x,l)) -> false()
      is_empty(nil()) -> true()
      tl(cons(x,l)) -> l
  - Signature:
      {append/2,hd/1,ifappend/3,is_empty/1,tl/1} / {cons/2,false/0,nil/0,true/0}
  - Obligation:
      innermost runtime complexity wrt. defined symbols {append,hd,ifappend,is_empty,tl} and constructors {cons
      ,false,nil,true}
WORST_CASE(?,O(n^1))