lib(queues)


    In this package, a queue is represented as a term Front-Back,  where
    Front  is  a list and Back is a tail of that list, and is normally a
    variable.  join_queue will only work when the Back  is  a  variable,
    the  other routines will accept any tail.  The elements of the queue
    are the list difference, that is, all the elements starting at Front
    and stopping at Back.  Examples:

	[a,b,c,d,e|Z]-Z	    has elements a,b,c,d,e
	[a,b,c,d,e]-[d,e]   has elements a,b,c
	Z-Z		    has no elements
	[1,2,3]-[1,2,3]	    has no elements



