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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 provStacks(self, offs, size):
        '''
        Returns a stream of provenance stacks at the given offset
        '''
        for _, iden in self.provseq.slice(offs, size):
            stack = self.getProvStack(iden)
            if stack is None:
                continue
            yield (iden, stack)