The "notational second derivative" is true only when the function 𝑓(𝑥) is of a very specific form
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so what's the basis for the solution space?
You usually only have a basis if the equation is linear. Think of he solution more as a (nonlinear) manifold of solutions.
Phew... I am onto my second beer, half asleep on the couch so I was starting to question myself :P
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