var float x[1..6,1..6] in 0..1;
maximize 
   x[1,3]+x[1,5]+x[2,2]+x[2,4]+x[2,5]+x[3,1]+x[3,6]+x[4,3]+x[5,5]+x[6,5]+x[6,6]

subject to {
   x[1,3]+x[1,5]<= 1;
   x[2,2]+x[2,4]+x[2,5]<=1;
   x[3,1]+x[3,6]<=1;
   x[6,5]+x[6,6]<=1;
   x[1,3]+x[4,3]<=1;
   x[1,5]+x[2,5]+x[5,5]+x[6,5]<=1;
   x[3,6]+x[6,6]<=1;};