
62 Polytope Projects
In the lifted binary tree y covers x if it is obtained by adjoining a single
“0” or “1” to the end of x. On the other hand x is covered by y in Binword
if it is obtained from y by removing a single letter, but not the fi rst. For
example 101001 covers 11001, 10001, 10101 and 10100.
Figure 3.14a shows the U-graph while Fig. 3.14b shows the D-graph.
U denotes the “up” operator generating the U-graph while D denotes
the “down” operator generating the D-graph.
An example will show how the differential model works to generate
the trees.
Let us consider the element (11) of the dual graphs. Using Fig. 3.14a or
Fig. 3.14b we can perform ...