Evaluate Function variable in RPN mode?

[Han]

F1 behaves like a program. In RPN, commands are typed as: COMMAND(n) where the n designates the number of arguments for COMMAND. Suppose F1(X):=2*X^2-4. If you type 9 ENTER F1(1) then it executes F1 as a program using 1 argument, namely the 9 on the stack. Unlike the other commands where one can leave off the "(1)" in the case of a single argument, you must explicitly specify "F1(1)" (from what I can tell). Typing F1 by itself recalls the formula for F1 as I'm sure you already found out.