If a representative has been appointed, notifications must be addressed to him. If several such representatives have been appointed for a single interested party, notification to any one of them is sufficient. If several persons are joint applicants for or proprietors of a patent or have acted in common in filing notice of opposition or intervention and have not appointed a common representative, notification of one person, viz. the person referred to in Rule 151, will again be sufficient. If several interested parties have a common representative, notification of a single document to the common representative is sufficient.