MAYBE
* Step 1: Failure MAYBE
  + Considered Problem:
      - Strict TRS:
          a__U11(X1,X2) -> U11(X1,X2)
          a__U11(tt(),N) -> mark(N)
          a__U21(X1,X2,X3) -> U21(X1,X2,X3)
          a__U21(tt(),M,N) -> s(a__plus(mark(N),mark(M)))
          a__and(X1,X2) -> and(X1,X2)
          a__and(tt(),X) -> mark(X)
          a__isNat(X) -> isNat(X)
          a__isNat(0()) -> tt()
          a__isNat(plus(V1,V2)) -> a__and(a__isNat(V1),isNat(V2))
          a__isNat(s(V1)) -> a__isNat(V1)
          a__plus(N,0()) -> a__U11(a__isNat(N),N)
          a__plus(N,s(M)) -> a__U21(a__and(a__isNat(M),isNat(N)),M,N)
          a__plus(X1,X2) -> plus(X1,X2)
          mark(0()) -> 0()
          mark(U11(X1,X2)) -> a__U11(mark(X1),X2)
          mark(U21(X1,X2,X3)) -> a__U21(mark(X1),X2,X3)
          mark(and(X1,X2)) -> a__and(mark(X1),X2)
          mark(isNat(X)) -> a__isNat(X)
          mark(plus(X1,X2)) -> a__plus(mark(X1),mark(X2))
          mark(s(X)) -> s(mark(X))
          mark(tt()) -> tt()
      - Signature:
          {a__U11/2,a__U21/3,a__and/2,a__isNat/1,a__plus/2,mark/1} / {0/0,U11/2,U21/3,and/2,isNat/1,plus/2,s/1,tt/0}
      - Obligation:
          innermost runtime complexity wrt. defined symbols {a__U11,a__U21,a__and,a__isNat,a__plus
          ,mark} and constructors {0,U11,U21,and,isNat,plus,s,tt}
  + Applied Processor:
      MI {miKind = Automaton Nothing, miDimension = 3, miUArgs = NoUArgs, miURules = NoURules, miSelector = Nothing}
  + Details:
      Incompatible
MAYBE