Functional differential equation.
Let's see who is actually smart on /prog/, find a general solution to this functional differential equation.
f ''(x) = f(f(x)) and there are general solutions
In other words find a function whose 2nd derivative is equal to the same function evaluated at all the points that make that function up.
For example f(f(x)) = ? when f(x) = x^2
is for x=2 ----> f(f(4)) ----> f(4) = 16 ----> f(16) = 256 and this has to be equal to its 2nd derivative
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