Sony PRS-T1 User Manual page 131

Note
 If you have deleted an item from [Books], it will be
automatically removed from all of the collections with
which it was associated.
 Removing items from a collection does not delete them
from the Reader or their stored locations.
Tip
 You can remove all items at once. After completing Step 1
above, press the
Table of Contents
(Menu) button
Using Collections

[Select All].
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