MAYBE
* Step 1: Failure MAYBE
  + Considered Problem:
      - Strict TRS:
          ++(x,nil()) -> x
          ++(++(x,y),z) -> ++(x,++(y,z))
          ++(nil(),y) -> y
          flatten(++(x,y)) -> ++(flatten(x),flatten(y))
          flatten(++(unit(x),y)) -> ++(flatten(x),flatten(y))
          flatten(flatten(x)) -> flatten(x)
          flatten(nil()) -> nil()
          flatten(unit(x)) -> flatten(x)
          rev(++(x,y)) -> ++(rev(y),rev(x))
          rev(nil()) -> nil()
          rev(rev(x)) -> x
          rev(unit(x)) -> unit(x)
      - Signature:
          {++/2,flatten/1,rev/1} / {nil/0,unit/1}
      - Obligation:
          innermost runtime complexity wrt. defined symbols {++,flatten,rev} and constructors {nil,unit}
  + Applied Processor:
      NaturalPI {shape = Mixed 3, restrict = NoRestrict, uargs = UArgs, urules = URules, selector = Nothing}
  + Details:
      Incompatible
MAYBE