please explain step by step

2. (10 pts) In order to create a truth table for a compound proposition containing n logical vari- ables, it is necessary to list in rows all possible combinations of T and F values. The following recursive procedure TF_list returns a list of strings representing all combinations of T and F values for n variables, n 2 1. The procedure uses the result for n - 1 variables to build the list for n variables. procedure TF_list (n: integer) if n=1 then return . . else prev_list = TF_list (n-1) return For n = 2, TF_list returns {TT, TF, FT, FF). For n = 3, TF_list returns {TTT, TTF, TFT, TFF, FTT, FTF, FFI, FFF). Describe in words (or pseudocode) what is missing from the above code. (Assume that it is easy to create, manipulate, and return lists in this language.)