when tcollect goes (sorta) buggy....

[quinyu]

In fact, the likely best solution would be an application similar to 50g's EQW, allowing selection of subexpressions and manipulate only those; or perhaps an interactive simplify/manipulate app where you could go step-by-step, and optionally influence how the next step is handled (in a pop-up menu or dynamic soft menu, perhaps.)

This, seeing that the Prime is aimed mainly at students (from what I hear), would have a multitude of benefits, first of which that they'd actually understand what's going on, also be able to choose the rewrites they are familiar with.

Then, for the transforms, I would leave the option to use the "nasty" trigonometric functions also accessible. "Nasty" meaning the cotangent, the secant and the cosecant - in many CAS systems they're much underused. I know there are other trigonometric functions (versine and its relatives, or the chord function) that many people did not even hear about; I'd not include those since likely the teachers would also get dumbfounded on them (even if they can produce very compact formulae, and in specialist fields, such as navigation, they are still used.)

But either way, thank you for any effort put into this - I am sure many users will welcome whatever improvements or changes they will receive in this bit of the calculator.