资料来源 : Free On-Line Dictionary of Computing

directed set
     
         A {set} X is directed under some {relation}, <= (less
        than or equal), if it is non-empty and if for any two elements
        x and y there exists an element z such that x <= z and y <= z.
        I.e. all pairs have an {upper bound}.
     
        (1994-11-11)