# $f(a(x))=f(x)$ - useful formula

I read "Functional Equations and also How to Solve Them" by Small and also the list below comment turns up without much validation on p. 13:

If $a(x)$ is an involution, after that $f(a(x))=f(x)$ has as remedies $f(x) = T\,[x,a(x)]$, where $T$ is an approximate symmetrical function of $u$ and also $v$.

I was asking yourself why this held true (it benefits instances I've attempted, yet I am not exactly sure $(1)$ just how to confirm this and also $(2)$ if there's anything noticeable looking at me in the face below).

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2019-05-05 23:21:53
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