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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_all_modified_on(chebi_ids):
    '''Returns all modified on'''
    all_modified_ons = [get_modified_on(chebi_id) for chebi_id in chebi_ids]
    all_modified_ons = [modified_on for modified_on in all_modified_ons
                        if modified_on is not None]
    return None if len(all_modified_ons) == 0 else sorted(all_modified_ons)[-1]