def METHOD_NAME(self, var_list):
    """Initialize optimizer variables.
    Lion optimizer has one variable `momentums`.
    Args:
        var_list: list of model variables to build Lion variables on.
    """
    if self.built:
        return
    super().METHOD_NAME(var_list)
    self._momentums = []
    for var in var_list:
        self._momentums.append(
            self.add_variable_from_reference(
                reference_variable=var, name="momentum"
            )
        )