<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _check_restart_params(self, restart_strategy, min_beta, s_greedy, xi_restart):
 r""" Check restarting parameters This method checks that the restarting parameters are set and satisfy the correct assumptions. It also checks that the current mode is regular (as opposed to CD for now). Parameters restart_strategy: str or None name of the restarting strategy. If None, there is no restarting. Defaults to None. min_beta: float or None the minimum beta when using the greedy restarting strategy. Defaults to None. s_greedy: float or None. parameter for the safeguard comparison in the greedy restarting strategy. It has to be > 1. Defaults to None. xi_restart: float or None. mutlitplicative parameter for the update of beta in the greedy restarting strategy and for the update of r_lazy in the adaptive restarting strategies. It has to be > 1. Defaults to None. Returns ------- bool: True Raises ------ ValueError When a parameter that should be set isn't or doesn't verify the correct assumptions. """


        if restart_strategy is None:
            return True

        if self.mode != 'regular':
            raise ValueError('Restarting strategies can only be used with '
                             'regular mode.')

        greedy_params_check = (min_beta is None or s_greedy is None or
                               s_greedy <= 1)

        if restart_strategy == 'greedy' and greedy_params_check:
            raise ValueError('You need a min_beta and an s_greedy > 1 for '
                             'greedy restart.')

        if xi_restart is None or xi_restart >= 1:
            raise ValueError('You need a xi_restart < 1 for restart.')

        return True