pro·lu·sion /proˈluʒən/
  序幕,序樂,開場白,預演
  Pro·lu·sion n.  A trial before the principal performance; a prelude; hence, an introductory essay or exercise. “Domestic prolusions.”
     Her presence was in some measure a restraint on the worthy divine, whose prolusion lasted.   --Sir W. Scott.
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  prolusion
       n 1: a short introductory essay preceding the text of a book
            [syn: foreword, preface]
       2: exercising in preparation for strenuous activity [syn: warm-up,
           tune-up]