For qin friends who are interested in the study of [Flowing Water]... This picture is showing a paragraph from Mr. 查阜西's research of [張孔山流水] 傳本考異 in June 9, 1957.
"諸譜亦間有之, 但只載首尾, 中缺滾拂. ... 非古人之不傳滾彿也, 時滾彿一段, 可以意會, 不可言傳." -- the "72 gun fu" part was omitted out from many qin tablature, not because ancient masters didn't teach this part, it is so difficult that can only be sensed but not explained.
Until Taoist priest Zhang Kong-shan (who was teaching qin at Si-chuan Provence between 1851-1894) and his pupils started to try to write down the techniques of this missing part.
Zhang did not invent the "72 gun fu" but learned from his teacher, 馮彤雲 Feng Tong-yun. According to Zha Fu-xi, Feng did not create the "72 gun fu" either. It should be already existed since then, and since it is so complicated that can only be taught by oral explanation and physical demonstration.
The foot note for #1 is : 見張孔山傳[百瓶齋流水譜]抄本和楊時百[琴學叢書] 刻本.