Written evidence could include the supply of information, or the production of a document or of a sworn statement. To take some examples:

To rebut an allegation by the examiner of lack of inventive step, the applicant might supply information as to the technical advantages of the invention. Again he might produce a sworn statement, either from himself or from an independent witness, purporting to show that workers in the art have been trying for a long time unsuccessfully to solve the problem with which the invention is concerned, or that the invention is a completely new departure in the relevant art.