(a) The source code in R5RS,
(b) 1-2 page description of your algorithm and its complexity as an ASCI text document, MS Word document, or a PDF file. Since the program you have to write is short, the description of the algorithm and the complexity analysis carry significant weight.
Write a function plus-minus in Scheme that takes a list L of one or more positive integers (duplicate are possible) and other auxiliary numeric parameters of your choice. Zero is not included in the list. The list L is flat, i.e., it does not contain sublists. The function plus-minus returns #t if it is possible to place plus or minus signs in front of each positive integer (including the first one) in the list so that the resulting arithmetic expression equals one of the positive integers in the list L. Otherwise, the function returns #f.