Ok, this is how --wrt-author sorts your example:
(Original example transposed so that variable width fonts don't play
havoc with the layout)
a10 b9
| \ |
a9 b8
| |
a8 b7
| |
a7 b6
| / |
a6 b5
| \ |
a5 b4
| |
a4 b3
| \ |
a3 b2
| |
a2 b1
| /
a1
with respect to a and b respectively
A B
| b9 | b9
^ a10 ^ a10
| b8 | a9
| b7 | a8
| b6 | a7
| b5 ^ b8
^ a9 | b7
| a8 | b6
| a7 | a6
| a6 | a5
| b4 | a4
| b3 | a3
^ a5 | a2
| a4 ^ b5
| b2 | b4
| b1 | b3
^ a3 | b2
| a2 | b1
= a1 = a1
In otherwords, B doesn't see any of A's changes after a1 until b6,
whereas A sees some of B's changes at a4 and some at a6, then not
again until a10.
jon.