There was some question whether it could be proven with trigonometric methods which is what they did.
Now it’s cheating to simply let a = c*cos(x) and b = c*sin(x) and thereby prove that c^2 = a^2 + b^2.
There was some concern that their proof was just a dressed up version of the above.
Apparently it wasn’t, and the proof stands.
Someone else proved it with trigonometric methods some years ago, so what they did is not earth-shattering but it was insightful.
Thank you for thee information you provided, which answered the question I had, and quite clearly I might add. 🙂👍