Which features are known and hence to be included in the preamble has to be decided in the light of the objective facts of the case (T 6/81, OJ 1982, 183).
In T 13/84 (OJ 1986, 253) the board considered it could not be accepted as a general rule that the piece of prior art used for the preamble of the claim should be concerned with the same problem as the invention (likewise T 287/02). Generally, the apparatus or process constituting the prior art which was nearest to the invention would have to figure in the preamble of the claim, stating such features of it as were necessary for the definition of the claimed subject-matter and which were in combination already part of this prior art (see also T 897/90). R. 29 EPC 1973 (like R. 43 EPC) made no reference to the necessity or desirability that the characterising portion of the claim should fairly set out the inventive step. It was the subject-matter of the claim as a whole which embodied the invention and the inventive step involved. See also T 886/91, T 157/93.
T 850/90 confirmed that examination for inventive step should also take account of the features in the preamble, since the invention was defined by the claims as a whole. Likewise, in T 980/95 it was held that there was no explicit requirement in R. 29(1)(a) EPC 1973 that a claim in two‑part form be set up on the basis of the "closest" prior art, since the rule made no reference to the necessity or desirability for the characterising portion of the claim to set out the inventive step. Basing the two‑part form on a particular state of the art which later turned out not to be the "closest" state of the art for the assessment of inventive step did not in itself contravene R. 29(1)(a) EPC 1973.
In decision T 688/91 (discussed in this chapter II.A.3.3.) the board took the view that there was a breach of R. 29 and Art. 84 EPC 1973 where an incorrect distinction was made between the preamble and the characterising portion (likewise T 181/95).