We may build a very big matrix where we have the time horizon for the first machine, the second machine and for the third machine. And this is for the blue machine, the yellow machine and the red machine. The ones in the upper-left part of the matrix are possible schedules of the first job on the first machine. The ones in the upper-central part of the matrix are possible schedules of the second job on the first machine and the ones in the upper-right part of the matrix are possible schedules of the third job on the first machine. The same can be said for the time horizon related to the second machine and for the third machine. Since each row is a particular time and each machine can process at most one operation at a time, we can choose columns, i.e. schedules, with at most one 1 in each row.