A set s, a subset of D, isscott-closed if (1) If Y is a subset of s and Y isdirected then lub Y is in s and (2) If y <= s in s then y is in s. I.e. a scott-closed set contains the lubs of itsdirectedsubsets and anything less than any element. (2) says that s is downward closed (or left closed). ("<=" is written in LaTeX assqsubseteq). (1995-02-03)