HP 50g Graphing Calculator - Manual (Page 271)

Page 8-14
to replace the plus sign (+) with ADD:
Next, we store the edited expression into variable @@@G@@@:
Evaluating G(L1,L2) now produces the following result:
As an alternative, you can define the function with ADD rather than the plus
sign (+), from the start, i.e., use
DEFINE('G(X,Y)=(X DD 3)*Y') :
You can also define the function as G(X,Y) = (X--3)*Y.