MAYBE
* Step 1: Failure MAYBE
  + Considered Problem:
      - Strict TRS:
          U11(mark(X1),X2) -> mark(U11(X1,X2))
          U11(ok(X1),ok(X2)) -> ok(U11(X1,X2))
          U12(mark(X)) -> mark(U12(X))
          U12(ok(X)) -> ok(U12(X))
          U21(mark(X)) -> mark(U21(X))
          U21(ok(X)) -> ok(U21(X))
          U31(mark(X1),X2) -> mark(U31(X1,X2))
          U31(ok(X1),ok(X2)) -> ok(U31(X1,X2))
          U41(mark(X1),X2,X3) -> mark(U41(X1,X2,X3))
          U41(ok(X1),ok(X2),ok(X3)) -> ok(U41(X1,X2,X3))
          U42(mark(X1),X2,X3) -> mark(U42(X1,X2,X3))
          U42(ok(X1),ok(X2),ok(X3)) -> ok(U42(X1,X2,X3))
          active(U11(X1,X2)) -> U11(active(X1),X2)
          active(U11(tt(),V2)) -> mark(U12(isNat(V2)))
          active(U12(X)) -> U12(active(X))
          active(U12(tt())) -> mark(tt())
          active(U21(X)) -> U21(active(X))
          active(U21(tt())) -> mark(tt())
          active(U31(X1,X2)) -> U31(active(X1),X2)
          active(U31(tt(),N)) -> mark(N)
          active(U41(X1,X2,X3)) -> U41(active(X1),X2,X3)
          active(U41(tt(),M,N)) -> mark(U42(isNat(N),M,N))
          active(U42(X1,X2,X3)) -> U42(active(X1),X2,X3)
          active(U42(tt(),M,N)) -> mark(s(plus(N,M)))
          active(isNat(0())) -> mark(tt())
          active(isNat(plus(V1,V2))) -> mark(U11(isNat(V1),V2))
          active(isNat(s(V1))) -> mark(U21(isNat(V1)))
          active(plus(N,0())) -> mark(U31(isNat(N),N))
          active(plus(N,s(M))) -> mark(U41(isNat(M),M,N))
          active(plus(X1,X2)) -> plus(X1,active(X2))
          active(plus(X1,X2)) -> plus(active(X1),X2)
          active(s(X)) -> s(active(X))
          isNat(ok(X)) -> ok(isNat(X))
          plus(X1,mark(X2)) -> mark(plus(X1,X2))
          plus(mark(X1),X2) -> mark(plus(X1,X2))
          plus(ok(X1),ok(X2)) -> ok(plus(X1,X2))
          proper(0()) -> ok(0())
          proper(U11(X1,X2)) -> U11(proper(X1),proper(X2))
          proper(U12(X)) -> U12(proper(X))
          proper(U21(X)) -> U21(proper(X))
          proper(U31(X1,X2)) -> U31(proper(X1),proper(X2))
          proper(U41(X1,X2,X3)) -> U41(proper(X1),proper(X2),proper(X3))
          proper(U42(X1,X2,X3)) -> U42(proper(X1),proper(X2),proper(X3))
          proper(isNat(X)) -> isNat(proper(X))
          proper(plus(X1,X2)) -> plus(proper(X1),proper(X2))
          proper(s(X)) -> s(proper(X))
          proper(tt()) -> ok(tt())
          s(mark(X)) -> mark(s(X))
          s(ok(X)) -> ok(s(X))
          top(mark(X)) -> top(proper(X))
          top(ok(X)) -> top(active(X))
      - Signature:
          {U11/2,U12/1,U21/1,U31/2,U41/3,U42/3,active/1,isNat/1,plus/2,proper/1,s/1,top/1} / {0/0,mark/1,ok/1,tt/0}
      - Obligation:
          innermost runtime complexity wrt. defined symbols {U11,U12,U21,U31,U41,U42,active,isNat,plus,proper,s
          ,top} and constructors {0,mark,ok,tt}
  + Applied Processor:
      MI {miKind = Automaton Nothing, miDimension = 3, miUArgs = NoUArgs, miURules = NoURules, miSelector = Nothing}
  + Details:
      Incompatible
MAYBE