reserve TS for 1-sorted,
  K, Q for Subset of TS;
reserve TS for TopSpace,
  GX for TopStruct,
  x for set,
  P, Q for Subset of TS,
  K , L for Subset of TS,
  R, S for Subset of GX,
  T, W for Subset of GX;

theorem Th60:
  P is open & P is nowhere_dense implies P = {}
proof
  assume that
A1: P is open and
A2: P is nowhere_dense and
A3: P <> {};
  P meets P` by A1,A2,A3,Th45;
  hence contradiction by XBOOLE_1:79;
end;
