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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 concepts(self):
 """ Return all existing concepts, i.e. dimensions, measures and attributes within the model. """

        for measure in self.measures:
            yield measure
        for aggregate in self.aggregates:
            yield aggregate
        for dimension in self.dimensions:
            yield dimension
            for attribute in dimension.attributes:
                yield attribute