preemptive or preemtive ?

hi,

Who can tell me should it be preemptive or preemtive? And
what is the EXACT meaning?

thanks.
-- 
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Tao Jiang     Visiting Engineer,               E40-369, CECI, MIT
phone:        (617)-253-3514(o)  (617)-576-9665 (h)
email:   jiangt@ceci.mit.edu    URL:  http://www.mech.pku.edu.cn 
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Received on Tuesday, 16 January 1996 11:58:46 UTC