訂正日: 2006/08/29訂正理由: -訂正箇所: 引用文献情報訂正内容: Right : 1) ((pq))=p01q23-p02q13+p03q12+p12q03-p13q02+p23q01. 2) As for the details, reference is to be made to our paper: Takeda, K., On line congruence, I, Tôhoku, 44 (1938), 356-69. 3) As for the details and notations, references are to be made to our paper: Takeda, K., On line congruence, II, Tôhoku, 45 (1938), 103-110. 4) Here we exclude the trivial cases, where the focal surfaces are reduced to special forms, that is, the cases F11=G11=0, F11F22=0 and G11=G22=0. 5) Bompiani, E., Proprietà differenziale caratteristica delle superficie che rappresentano la totalità delle curve piane algebriche di dato ordine, Lincei, 30 (1921), 248-51.