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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 get_notebook_rel_path(pkg=None):
 """Get the path of a notebook, relative to the current soruce package"""

    pkg = pkg or open_source_package()
    pkg_path = str(pkg.package_url.fspath)
    nb_path = get_notebook_path()

    return nb_path.replace(pkg_path, '').strip('/')