def NUTS_down(NUTS):
    """
    For a given NUTS-region, finds the corresponding region its is part of 
    
    Arguments:
        *NUTS* (string) -- name of the NUTS region (e.g NL413 )
    
    Returns:
        *NUTS_lower* (string) -- name of the NUTS region one level lower (e.g. NL41)
    """
    if len(NUTS) <= 2: #the NUTS-0 level (country) is the lowest level and has length 2
        raise ValueError("Cannot aggregate {} to a lower NUTS-level".format(NUTS))
    #would be nice to check if the output exists as a region
    return str(NUTS)[:-1]