Professor Cheng is said to have considered “Single Whip” to be one of the most important movements to practice and cited seeking the straight from the curve when describing this movement.2
In the martial application of “Single Whip,” your right wrist contacts the outside of the opponent’s incoming striking left wrist.
Your hand drapes over his left wrist, circles his incoming arm out to his left, and then strikes him in a straight-line motion (the straight from the curve).
I can’t think of any other movement in the form that does that. “Single Whip” is truly unique and whip-like when done as a fajin. Parting the “Wild Horse’s Mane” is somewhat similar when done as I was taught by Sam Chin Fan-siong.
https://www.chuckrowtaichi.com/StraightFromCurve.html
Interesting apps,,,for single whip...
Our way a little different...more about controlling the space, either before or at the point of contact.