MAYBE We are left with following problem, upon which TcT provides the certificate MAYBE. Strict Trs: { purge(nil()) -> nil() , purge(.(x, y)) -> .(x, purge(remove(x, y))) , remove(x, nil()) -> nil() , remove(x, .(y, z)) -> if(=(x, y), remove(x, z), .(y, remove(x, z))) } Obligation: innermost runtime complexity Answer: MAYBE The input cannot be shown compatible Arrrr..