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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 ls_dir(base_dir):
 """List files recursively."""

    return [
        os.path.join(dirpath.replace(base_dir, '', 1), f)
        for (dirpath, dirnames, files) in os.walk(base_dir)
        for f in files
    ]