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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 _find_proj_root():
 # type: () -> Optional[str] """ Find the project path by going up the file tree. This will look in the current directory and upwards for the pelconf file (.yaml or .py) """

    proj_files = frozenset(('pelconf.py', 'pelconf.yaml'))
    curr = os.getcwd()

    while curr.startswith('/') and len(curr) > 1:
        if proj_files & frozenset(os.listdir(curr)):
            return curr
        else:
            curr = os.path.dirname(curr)

    return None