Even though a reasonable amount of trial and error is permissible when it comes to sufficiency of disclosure, e.g. in an unexplored field or where there are many technical difficulties, the skilled person has to have at his disposal, either in the specification or on the basis of common general knowledge, adequate information leading necessarily and directly towards success through the evaluation of initial failures (T 226/85, OJ 1988, 336; following T 14/83, OJ 1984, 105; T 48/85, T 307/86 and T 326/04). Where the skilled person can only establish by trial and error whether or not his particular choice of numerous parameters will provide a satisfactory result, this amounts to an undue burden (T 32/85). Nor can sufficiency of disclosure be acknowledged, if, for an invention which goes against prevailing technical opinion, the patentee fails to give even a single reproducible example (T 792/00. See also T 397/02, T 1440/07 and T 623/08).