Before:
XXXXXXXXXXXXXX = result-set 0
-------------- = result-set 1
-------------- = result-set 2

After adding a:
XX---------XXX = result-set 0
--XXXXXXXXX--- = result-set 1
-------------- = result-set 2

After adding b:
XX---------XXX = result-set 0
--XXX---XXX--- = result-set 1
-----XXX------ = result-set 2