Under R. 104 EPC, a fundamental procedural defect may have occurred where the board of appeal, contrary to Art. 116 EPC, failed to arrange for the holding of oral proceedings requested by the petitioner, or decided on the appeal without deciding on a request relevant to that decision. What is not defined by the Implementing Regulations does not qualify as a procedural defect within the meaning of Art. 112a(2)(d) EPC (R 16/09; see in this chapter V.B.3.4.2).