In mode 7, the intonation torculus (e.g. in the introit psalm tone) in the modern notation edition of the Liber, as well as accompaniment books according to the Solesmes method, has the ictus marked on the upper (second) note of the torculus, but there is usually no indication for ictus placement in this neume in the Gregorian notation editions. I understand the semiological reasons for placing the ictus on the upper note (it is a torculus initio debilis in the MSS), but can anyone point me to an explanation of the rhythmic interpretation of this figure strictly according to the Solesmes method, in some method book perhaps?