QUESTION
For example, I hate that Mathematica uses Pochhammer symbol in outputs and prefer all the expressions in Gamma function. How can I ban usage of Pochhammer? I also want all outputs to use HurwitzZeta rather than Zeta.
In another instance I want the results to use my own variant of Polygamma function (modified). How can I mandate its usage when possible?
ANSWER
You may try for example something like:
f[e_] := 100 Count[e, _Pochhammer, {0, Infinity}] + LeafCount[e];
FullSimplify[Pochhammer[k, n], ComplexityFunction -> f]
(*
->Gamma[k + n]/Gamma[k]
*)
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