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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 prerequisites(self):
 """ Iterates through the inputs of the pipelinen and determines the all prerequisite pipelines """

        # Loop through the inputs to the pipeline and add the instancemethods
        # for the pipelines to generate each of the processed inputs
        prereqs = defaultdict(set)
        for input in self.inputs:  # @ReservedAssignment
            spec = self._study.spec(input)
            # Could be an input to the study or optional acquired spec
            if spec.is_spec and spec.derived:
                prereqs[spec.pipeline_getter].add(input.name)
        return prereqs