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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:

def _initialize_non_fluents(self):
        '''Returns the non-fluents instantiated.'''
        non_fluents = self.rddl.domain.non_fluents
        initializer = self.rddl.non_fluents.init_non_fluent
        self.non_fluents = self._initialize_pvariables(
            non_fluents,
            self.rddl.domain.non_fluent_ordering,
            initializer)
        return self.non_fluents