The number of ways 
of finding a subrectangle with an 
rectangle can be computed
by counting the number of ways in which the upper right-hand corner can be selected
for a given lower left-hand corner. For a lower left-hand corner with coordinates
, there are 
possible upper right-hand corners, so
 |  |  |
(1)
|
 |  |  |
(2)
|
Equivalently, 
is the number of ways of picking two lines out of sets of 
and 
lines, giving
 |  |  |
(3)
|
 |  |  |
(4)
|
as before. Particular tilings are shown above for 
and 
rectangles.
