52As has been recognised by case-law, the requirement of a handwritten signature for the purposes of the first subparagraph of Article 43(1) is designed, for reasons of legal certainty, to ensure the authenticity of the application and to eliminate the risk that that document is not in fact the work of the author authorised for that purpose. That requirement must therefore be regarded as an essential procedural rule and be applied strictly, so that failure to comply with it leads to the inadmissibility of the action (Case T-223/06 PParliament v Eistrup [2007] ECR II-1581, paragraph 51).