reserve GX for TopSpace;
reserve A, B, C for Subset of GX;
reserve TS for TopStruct;
reserve K, K1, L, L1 for Subset of TS;

theorem Th19:
  A is connected implies Cl A is connected
proof
A1: A c= Cl A by PRE_TOPC:18;
  assume A is connected;
  hence thesis by A1,Th18;
end;
