def restore_plasticity_state(self):
self.plastic = self._plasticity_setting_stack.pop()<EOL>
Re-enable plasticity of internal state after an
override_plasticity_state call.

This function should be implemented by all subclasses to
remove the effect of the most recent override_plasticity_state call,
i.e. to reenable changes to the internal state, without any
lasting effect from the time during which plasticity was disabled.

By default, simply restores the last saved value of the
'plastic' parameter.