MAYBE
* Step 1: Failure MAYBE
  + Considered Problem:
      - Strict TRS:
          -(x,0()) -> x
          -(s(x),s(y)) -> -(x,y)
          <=(0(),y) -> true()
          <=(s(x),0()) -> false()
          <=(s(x),s(y)) -> <=(x,y)
          f(0(),y,0(),u) -> true()
          f(0(),y,s(z),u) -> false()
          f(s(x),0(),z,u) -> f(x,u,-(z,s(x)),u)
          f(s(x),s(y),z,u) -> if(<=(x,y),f(s(x),-(y,x),z,u),f(x,u,z,u))
          if(false(),x,y) -> y
          if(true(),x,y) -> x
          perfectp(0()) -> false()
          perfectp(s(x)) -> f(x,s(0()),s(x),s(x))
      - Signature:
          {-/2,<=/2,f/4,if/3,perfectp/1} / {0/0,false/0,s/1,true/0}
      - Obligation:
          innermost runtime complexity wrt. defined symbols {-,<=,f,if,perfectp} and constructors {0,false,s,true}
  + Applied Processor:
      EmptyProcessor
  + Details:
      The problem is still open.
MAYBE