How does Maple send a plot to a ps file?

How would I generate all possible strings of letters from a given string of letters? (For example, if a given string of letters is "AA", then all possible strings of letters are "A" and "AA". If a given string of letters is "ABA", then all possible strings of letters in lexicographic order are "A", "AA", "AAB", "AB", "ABA", "B", "BA", "BAA".) I know that I first need to convert the string of letters to a list of letters, but I can't figure out the correct coding. Thanks for any advice!

How would I find and check 10 distinct solutions to the matrix equation Matrix(2, 4, {(1, 1) = 1, (1, 2) = 2, (1, 3) = 3, (1, 4) = 4, (2, 1) = 5, (2, 2) = 6, (2, 3) = 7, (2, 4) = 8}) Vector(4, {(1) = x[1], (2) = x[2], (3) = x[3], (4) = x[4]}) = Vector(2, {(1) = 10, (2) = 10}) ? I know that I need to use LinearSolve, but I'm not sure how to do it exactly...