Many thanks for that. I agree because at least it is internally consistent. Whereas from the NASA site
This additional force is called induced drag because it faces downstream and has been "induced" by the action of the tip vortices. It is also called "drag due to lift" because it only occurs on finite, lifting wings and varies with the square of the lift.
The emboldening is mine, and encouraged by your support I rather disagree with it. The Virginia article also focuses exclusively on the tip vortex issue, and ignores the mechanical issues.
To quote again from the NASA article
The derivation of the equation for the induced drag is fairly tedious and relies on some theoretical ideas which are beyond the scope of the Beginner's Guide.
Maybe someone who has endured the tedium can shed some light on this. Tip vortices, revectoring, or both ?