kill(all)$

van=facebook.com/LearningCalculus$

MN:transpose([n+m-2,n-2])+transpose([n+m-3,n-2]);

      assume MN = transpose([0,0])

solve(first(MN[1]-MN[2])=0,m);

a(m,n):=''(first(first(MN))=0);

solve(a(1/2,n),n);