In his book "The Philosophy of Recursive Thinking", German author Manfred Kopfer suggested a viable solution for Sisyphus' punishment. Every time Sisyphus reaches the top of the mountain, he breaks off a stone from the mountain and carries it down to the lowest point. This way, the mountain will eventually be levelled and the stone cannot roll down anymore. In Kopfers' interpretation, the solution turns the punishment by the gods into a test for Sisyphus to prove his worthiness for godlike deeds. If Sisyphus is able "to move a mountain", he shall be allowed to do what, otherwise, only gods are entitled to do.