In T 552/91 (OJ 1995, 100) the question arose as to whether and in what form protection could be obtained for groups of chemical substances and individual compounds whose originally disclosed structural formula proved incorrect. The applicant's main request was aimed at securing such protection by a further substance claim for the group of compounds with the structural formula subsequently found to be correct. This request was refused on the grounds that it would violate Art. 123(2) EPC 1973. The board held that the subsequently amended general formula gave the skilled person for the first time crucial information about the true chemical structure of the group of substances. This led to conclusions regarding properties that could be put to use. The information added to the application through the amendment of the general formula and relating to the true composition of the group of substances could not have been obtained from the application as originally filed (for decisions referring to T 552/91, see T 1074/97 and T 2003/07; for a further example of the correction of an error in a formula, see T 1728/07).