--load the nine first local digits images from the left.
zero_img = sol.surface.create("input_number/numbers/0.png"),
one_img = sol.surface.create("input_number/numbers/1.png") ,
two_img = sol.surface.create("input_number/numbers/2.png"),
three_img = sol.surface.create("input_number/numbers/3.png"),
four_img = sol.surface.create("input_number/numbers/4.png"),
five_img = sol.surface.create("input_number/numbers/5.png"),
six_img = sol.surface.create("input_number/numbers/6.png"),
seven_img = sol.surface.create("input_number/numbers/7.png"),
eight_img = sol.surface.create("input_number/numbers/8.png"),
nine_img = sol.surface.create("input_number/numbers/9.png"),