R. 43(1)(a) and (b) EPC (like R. 29(1)(a) and (b) EPC 1973) define the two-part form which a claim is to have where this is appropriate. Such claims must contain a statement indicating the designation of the subject-matter of the invention and those technical features which are necessary for the definition of the claimed subject-matter but which, in combination, form part of the prior art ("preamble"), and a characterising portion stating the technical features for which, in combination with the features stated in the first part, protection is sought. See also Guidelines F‑IV, 2 – November 2018 version.