Sequences: where do 'unused' numbers go in case of rollback

The Oracle-sequence-numeber can be accessed via :

Select <sequence_name>.nextval
from dual

When you do this in thwo separate sessions and one sessions is rolled back, where does the 'unused' sequence-numer go? Is it still available for use later?
And how can you 'return' a not-in-use sequence-number to the sequence-number pool?

Any help (or pointers to the right place in the Oracle-doc) is appreciated...

SWM Automatisering
Edward W. Vergragt
vergragt_at_inter.NL.net

programmatuur voor handel in bulk-goederen (commodities), gebaseerd op het Oracle RDBMS software for commodity-traders, trafficers, Oracle-based Received on Sun Oct 01 1995 - 00:00:00 CET