CAS command question

[parisse]

When you write L9:={ 'x+y = 4', 'x+y > 4', 'x+y ≥ 4', 'x+y<4', QUOTE(x+y ≤ 4) }; the right side of := is evaled, since all expressions are quoted, it will set L9 to { x+y = 4, x+y > 4, x+y ≥ 4, x+y<4, x+y ≤ 4 }, without quotes. If expressions inside the definition of L9 were not quoted, then x, y and inequations would have been evaled themselve, here they are not.
If you are writing L8(I):=left(L9(I)); then L9(I) is evaled, but this time nothing is quoted anymore and x,y and operators are evaled. You would have to double-quote the original input to avoid evaluation at this step.
DrD: you can not make something useful with a command that does not eval arguments except for a few exceptions (:= is an exemple of exception, it does not eval it's left argument). On the example above, left(L9(I)) would not do anything because L9(I) would not be replaced by the I-th element of L9.

This thread make me realize that there is probably a need to make a small FAQ about CAS expressions and evaluation (something I teach to some of my students). Unless there is already something good enough on the net, perhaps Han you know some interesting ressource? (wikipedia seems a little bit too short, Fateman's paper too long)