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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 uses_placeholder_y(ds):
 """If ``ds`` is a ``skorch.dataset.Dataset`` or a ``skorch.dataset.Dataset`` nested inside a ``torch.utils.data.Subset`` and uses y as a placeholder, return ``True``."""


    if isinstance(ds, torch.utils.data.Subset):
        return uses_placeholder_y(ds.dataset)
    return isinstance(ds, Dataset) and hasattr(ds, "y") and ds.y is None