<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def append_pdf(input_pdf: bytes, output_writer: PdfFileWriter):
 """ Appends a PDF to a pyPDF writer. Legacy interface. """

    append_memory_pdf_to_writer(input_pdf=input_pdf,
                                writer=output_writer)