Question 25
For integers $a, b, c$ and $d$ it is valid $a \gt b \gt c \gt d$ and
$$
(1-a)(1-b)(1-c)(1-d) = 10
$$
What values can take an expression $a + b - c - d$?
$$
(1-a)(1-b)(1-c)(1-d) = 10
$$
What values can take an expression $a + b - c - d$?