The f(x) algo is completely constructed at the "Smath stack" level. When the user function is called, it fetches the stack location .. blingbling ... done/plot. This is typical "scalar". After the plot, nothing remains, just the f(x) algo , can be re-used for next JoBlo. The derivative operator is "BookStyleAlgebraic"...does not recognise F(x)for plotting or else use... does not accept F(x). Differently, the integrate operator is a numerical aldo, thus recognises F(x). Note the transit triplet instruction Q(u) => Int(x) <= Int(z). The annoying derivative operator strikes again Lambert W(x) and any "if defined function". The Ridder derivative operator is needed.