This is a text description of schema4.gif.  

This figure illustrates deallocating all unused space, but specifying the KEEP keyword to retain 10K of the unused space. This is described in the text. 

The figure shows a table, dquon, before and after issuing the ALTER TABLE ... KEEP statement presented in the text.

Before, there are three extents of 10K, 20K, and 30K, respectively. After issuing the statement, there are two extents of 10K and 20K, respectively.