If in response to an invitation by the EPO as ISA additional search fees are paid and the additional searches reveal a further lack of unity within one of the inventions found initially ("a posteriori"), no further invitation to pay additional fees is issued and the international search is limited to the first invention of each further invention for which an additional fee was paid. If a cascading lack of unity of invention is likely to arise, the invitation to pay additional fees will contain a warning in that respect.