It is obvious that the step (a) of

It is obvious that the step (a) of Method 2 stands for a special case of step (a) of
Method 1. We may also ask students to show that with step (b) of Method 2, the
second and third rows will also be special cases of those described in step (b) of
Method 1. Finally, the rest of the grid is filled exactly the same way as in step (c)
of Method 1, in the form of