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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 sub(x, y, context=None):
 """ Return ``x`` - ``y``. """

    return _apply_function_in_current_context(
        BigFloat,
        mpfr.mpfr_sub,
        (
            BigFloat._implicit_convert(x),
            BigFloat._implicit_convert(y),
        ),
        context,
    )