reserve T for TopSpace;
reserve T for non empty TopSpace;
reserve F for Subset-Family of T;

theorem Th50:
  union(Int Cl F) c= Int Cl(union F)
proof
A1: Int(union Cl F) c= Int Cl(union F) by Th15,TOPS_1:19;
  union(Int Cl F) c= Int(union Cl F) by Th27;
  hence thesis by A1;
end;
