A European application must "relate to one invention only or to a group of inventions so linked as to form a single general inventive concept". The second of these alternatives, i.e. the single-concept linked group, may give rise to a plurality of independent claims in the same category provided these claims comply with Rule 29(2) (see III, 3.2 and III, 3.3), but the more usual case is a plurality of independent claims in different categories.