If a patent is so amended that a claim to a product is replaced by a claim to a method for producing the product, this change of category is allowable, provided that the method now claimed only results in the product previously claimed. As it is a fundamental principle of European patent law that the protection conferred by a product claim covers all methods for production of the product, the limitation to one of these methods cannot extend the protection conferred originally (see T 5/90 and T 54/90).