` \\ fs [arg0_def]       \\ fs [evaluate_def]       \\ rename [`_ = _::ys`] \\ Cases_on `ys` \\ fs [arg0_def]       \\ fs [evaluate_def]       \\ rename [`_ = _::_::ys`] \\ Cases_on `ys` \\ fs [arg0_def]       \\ fs [evaluate_def] 