D-----------|
/ \ |
/ \ |
/ C \ |
. / /|\ \ |
/ / | \ \ |
A--B | E--F |
\ \ | / / |
\ \|/ / |
\ G / |
\ / |
\ / |
H-----------|
Figure 1
Figure 1 is the basic "twin-triangle graph. Figure 1 can be expanded infinitely
by replacing a single vertex with three vertices. See an example in Figure 2
D-----------|
/ \ |
/ \ |
/ C \ |
. / /|\ \ |
/ / | \ \ |
A--B | E--F |
| \ | / | |
| \|/ | |
| G | |
| | |
I-----------K |
\ / |
\---J---/ |
|-----------|
Figure 2
In Figure 1, note that Face ABCEFD has two edges in common with Face ABGEFH.
The face vertex dual of Figure 1 will have parallel edges between the vertices
representing these two faces.
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