Scott-closed
A set S, a subset of D, is Scott-closed if
(1) If Y is a subset of S and Y is {directed} 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 its {directed}
subsets and anything less than any element. (2) says that S
is downward {closed} (or left closed).
("<=" is written in {LaTeX} as {\sqsubseteq}).
(1995-02-03)