Examination of the notice of opposition for admissibility 
Immediately after receiving the notice of opposition, the EPO will forward it to the proprietor. Then the admissibility of the opposition is checked. Deficiencies in the notice are communicated to the opponent. Deficiencies under Rule 77(1) must be remedied within the opposition period. Other remediable deficiencies must be corrected within a period specified by the EPO (generally two months). If the deficiencies noted are not corrected in due time, the notice of opposition is rejected as inadmissible.
Documents cited in support of the opposition or as evidence must be specified in the notice of opposition and should be filed at the same time. If not filed with the initial notice of opposition, all cited documents will be requested from the opponent within an additional time limit of two months. If the opponent fails to do so in due time, the opposition division may decide not to take any arguments based on them into account. 
Immediately after expiry of the opposition period or the period laid down for remedying deficiencies or presenting evidence, the patent proprietor is invited to file observations and, where appropriate, amendments within a period specified by the EPO (generally four months). Amendments are allowed only if they are occasioned by grounds for opposition under Article 100, including grounds not invoked by the opponent.
The EPO communicates notices of opposition and any letters filed during opposition proceedings to the other parties for information. However, the EPO does not automatically transmit copies of any documents annexed to notices of opposition or to letters which are available for inspection and download in the European Patent Register. 

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