原式=1-n-m+mn=1-(m+n)+mn=1-2+(-2)=-3
(1-m)(1-n)=1-(m+n)+mn=1-2-2=-3
=1-(m+n)+mn=1- 2- 2=-3
(1-m)(1-n)=1-n-m-mn=1-(n+m)+mn=1-2-2=-3
(1-m)(1-n)=1-n-m+mn=1-(m+n)+mn=1-2-2=-3