Added ToDo-list.

1911c3fe · Taddeus Kroes · 21f0710c · 1911c3fe
Commit 1911c3fe authored 13 years ago by Taddeus Kroes
--- a/TODO
+++ b/TODO
+ - The graph of "--ab + c" is also not valid:
+
+     -
+     │
+      +
+    ╭─┴╮
+    *  c
+   ╭┴╮
+   - b
+   │
+   a