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after having searched through many books and the documentation, I still do not have a clear definition of what the Hold..., Unevaluated, Defer, Inactivate operations do when considering the TreeForm of a Formula.

I would like to start by freezing a long formula and then activate and operate on certain parts of the tree before freezing them again.

What is the general procedure for that?

(e.g. for a nested expression like

    Z=Integrate[u/2x^2,x];
    a=3n
    G=Sum[n^2 a,{n,0,10}];
    F=Exp[Exp[Z + G]]

I would like to operate on G,a separately using only the last expression.)

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  • $\begingroup$ It would be nice to see what do you mean by "I would like to operate on G,a separately using only the last expression.)" on examples. $\endgroup$ – Kuba Aug 23 '18 at 15:34
  • $\begingroup$ I think that you probably should avoid assigning values to variables, instead using rules and ReplaceAll. E.g. Exp[Exp[Z+G]]/.G->Sum[n^2,{n,0,10}] $\endgroup$ – mikado Aug 23 '18 at 18:30

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