{ {1,3} , {2,4} }
--------
| |
|A |B
-----------------
| | |
| | |
| |
| |
--------------
A = {1,3}
B = {2,4}
The shadow cannot close without
altering the notation; this
notation is therefore undrawable.
{ {1,4}, {3,6}, {5,8}, {7,10}, {9,2} }
---5----
| |
|A |B
------D----------
| | |
| | |
| 8---C |
| |
--------------
A = {1,4}
B = {3,6}
C = {7,10}
D = {9,2}
The points 5 and 8 cannot meet to
form the crossing {5,8} and thus
this notation is also undrawable.

Charilaos Aneziris, aneziris@hades.ifh.de
Copyright 1995
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