Hi!
The author also researches the downwash and the vortices....in the 3D case. Pictures above show the 2D case, to illustrate how the phenomenon of lift is initially created by forward movement and down going movement of the stagnation point and showing, that then more air mass is flowing over the wing than underneath with the positive angle of attack. The solution for an infinite wing span (2D case) is without power and only delivers a force component crosswise to the flow. This also shows the video above by the way!
In the 3D case the vortices form as the result of pressure equalization at the edges of the wing. The vortices stay behind streamwise as the wing travels further in the direction of flight. Honestly, it is very complicated. But for me it really helped to understand, and this is a fact, that more air is flowing above the wing.....it is obvious and I have never seen it anywhere before in a book until I have found the explanations of Dr Send. The rest...is very mathematical.