using an app command in cas. (area)

[Angus]

Thank you! Is there a larger group of commands missing in the cataloge?

One more thing: area (lowercase) seems to require a functional notation of F1 if used in the original example. area(F1(x), x=0..1) works nicely. area(F1, x=0..1) and area(F1,X=0..1) fail. Is there a rule or explanation on when I have to type F1(x) and when F1 is sufficiant? In the example they show AREA(x^2-1,0,1) where the formula is clearly an expression and no function.... :-(

I can imagine that the area command, when called like area(F1(x),x=0..1) inserts 'x' into the function and therefore is valid under cas. Uppercase single 'X' is treated numerically (its home-value) which is why they are always forbidden under cas (if not used for a numerical value)? Well, is there any benefit from splitting the nomenclature but on the other hand blur their difference? I can type in F1(foo) and get foo^2-1. Which I am pleased with, but in the Function app F1 was defined as F1(X); so I am surprised that the capital X can be treated symbolically after all and replace X with foo.....

edit: I think I see the flaw in my thoughts... ANY function can insert anything as its argument, but if the inserted argument is a capitalized single letter variable like 'X' is has to be treated as a numerical value? ;-) Then only the question remains, why the apps use X wich seems to make things more complicated when it comes to cas interaction?