which, after crossing out the 1’s, 2’s, and 6’s in cells not in the preemptive set, produces the box
in the middle of Figure 5, where we observe the singleton 8 in c (1,8) , which means that 8 is the
only entry possible in c (1,8) and the 8 in the markup of c (3,8) must, therefore, be crossed out.
The result in the right-hand box is the revelation of the preemptive pair