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 operations of addition and multiplication, but now with the numbers −1, −2, −3, −4, 1, 2, 3, and 4 instead."
what observation is leoni trying to point out to luke?