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  writeandviewpage                                                      WNDWC
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  Function       Changes the video page to be both viewed and written on the
                 CRT.
  Syntax         void writeandviewpage( char pagenum );
  Remarks        If another video page is available, this routine will switch
                 to both view and write to that page.  It does nothing if
                 pagenum is already the currently written video page
                 (qvideo_page) and viewed page (videopage), or if pagenum is
                 invalid.  All wndwstats are swapped to exact same conditions
                 as before.
  Return value   None.
  Screens        All video pages.
  EOS            Restored to new page.