MAYBE

We are left with following problem, upon which TcT provides the
certificate MAYBE.

Strict Trs:
  { merge(x, nil()) -> x
  , merge(nil(), y) -> y
  , merge(.(x, y), .(u, v)) ->
    if(<(x, u), .(x, merge(y, .(u, v))), .(u, merge(.(x, y), v)))
  , if(true(), x, y) -> x
  , if(false(), x, y) -> x
  , ++(nil(), y) -> y
  , ++(.(x, y), z) -> .(x, ++(y, z)) }
Obligation:
  innermost runtime complexity
Answer:
  MAYBE

The input cannot be shown compatible

Arrrr..