Luke wants to play the 4 number game with the numbers 1, 2, 3, and 4 and the operations of addition, multiplication, and subtraction. leoni responds, "or we just could play the 4 number game with just the operation of addition and multiplication, but now with the numbers -1, -2, -3, -4, 1, 2, 3, 4 instead what observation is leoni trying to point out to luke?