hello. I am studying lisp and would like to ask for help.     There are numbers(mtext) assigned to different layers.     I want to sum these numbers by the same layer. ex)  Layer   /  Contents           AA     /     1.5                                                      AA   /   2.5           AA     /     1.0                          =>                        BB   /   2.0           BB     /     2.0     ITEM cells should always