IF-EXISTS :SUPERSEDE

["Bernard S. Greenberg" <BSG%SCRC-TENEX@MIT-MC.ARPA>]

    Date: Monday, 5 December 1983, 23:12-EST
    From: David A. Moon <Moon at SCRC-TENEX>
	Argument #2:
	  Given the primitives available to the file server in versionated
	  operating systems, it is impossible to implement this as proposed
	  without a window between determining the version number and opening
	  it for superseding.
    
    This argument is false.  The Tops-20/Tenex Chaosnet file server has
    no problem doing this without windows.  During the time between opening
    and closing, the old file is in an "open for reading" state that
    prevents anyone else from superseding it or renaming it.  Presumably other
    versionated operating systems may have comparable primitives.
Could you detail the sequence of operations?  The above is not sufficiently
clear.   When do you open the second file? Under what name?