The applicant may file a divisional application of his own volition (voluntary division). The most common reason, however, for filing a divisional application is to meet an objection under Art. 82 due to lack of unity of invention (mandatory division). If the examiner raises an objection due to lack of unity, the applicant is allowed a period (see VI, 11 and E-VIII, 1) in which to limit his application to a single invention. The limitation of the parent application has to be clear and unconditional. The communication inviting the applicant to limit the application due to lack of unity should therefore include a reference to the fact that if the application is not limited within the set time limit the application may be refused.