setting last_value of sequence

i've run into the situation where i need to set the last_value of a
sequence. can someone tell me how this is done?

--
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                                               | /"\
 john harrold                                  | \ / ASCII ribbon campaign
      jmh at member.fsf.org                    |  X  against HTML mail
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 What difference does it make to the dead, the orphans, and the homeless,
 whether the mad destruction is brought under the name of totalitarianism or
 the holy name of liberty and democracy?
 --Gandhi
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