% problem-set/topology/point.set/lemma19.clauses
% created : 08/08/88
% revised : 08/17/89

% description : 
% 
% lemma 19: yb is closed iff limit_pt_set(yb) is a subset of yb.

% representation : 
%
% See axioms.decl for a full explanation.

% denial: 

closed(B,X,T) | subset(limit_pt_set(B),B).
-closed(B,X,T) | -subset(limit_pt_set(B),B).