HP Prime: how to insert and save formulas in a sort of "Equation library"

[Dirk.nl]

Sorry for my late response and sorry if this had been explained before.
I do this in the following way.
Open Apps Window, select Solve App and save it with a new name based on Solve.
In the App window select the new Solve App. The focus of the Prime is now focused on this new Solve App.
Go to Program Editor (Shift Program) and select your "new name (APP)" and type EXPORT VarName, VarName, ...; Possibly several EXPORTs. Close the Progam editor. You can now use your variables in your new Solve App. They are visible and selectable in Vars, App, "new name", Program.
In this way you can possibly use the same variable names for different Apps, while they are not the same variables.