Users functions

   You can define useres functions. To do that, clic on the f(x) button,
   or enter "def" or "fonc" or "func" in the
   input zone. Then, enter a space and finaly, the function definition.

   Example : def f(x) = 3*x           -> define function f
   a = 6                    -> 6
   func g(x,y) = f(x)+a*y+2 -> define function g

   To eval an user function, enter its name and its parameters separated by coma,
   between parenthesis .

   Example :
                    def f(x) = 3*x           -> define function f
                    a = 6                    -> 6
                    func g(x,y) = f(x)+a*y+2 -> define function g
                    g(2,3)                   -> 26

   Users functions are saved in the users functions list. They can be seen
   with menu item Users functions.
   They are saved too in ENVARC:PSCalc/Fonctions/ if the tooltype 
   USEENV=YES.

   It's possible to copy a user function in the input zone by double-
   clicking on it's line or by simple-clicking on it's line followed by a clic on the
   [OK] button.