using an app command in cas. (area)

[parisse]

In the CAS, there is a strict distinction between a function and an expression. For example if you do f(x):=sin(x^2), f is a function (it maps x to sin(x^2)) whereas f(x) is an expression. HOME does not really distinguish between function and expression, and in addition HOME variables like X are assigned (but if you enter F1(X)=SIN(X^2) in the Function App, X is not replaced by the value). This probably make things a little easier for the user if you are doing something standard (in the Apps), but if you want to do something more elaborate, you must understand the distinction.