reserve S, R for 1-sorted,
  X for Subset of R,
  T for TopStruct,
  x for set;
reserve H for non empty multMagma,
  P, Q, P1, Q1 for Subset of H,
  h for Element of H;
reserve G for Group,
  A, B for Subset of G,
  a for Element of G;

theorem Th20:
  for T being non empty TopSpace, p being Point of T holds [#]T is
  a_neighborhood of p
proof
  let T be non empty TopSpace, p be Point of T;
  Int [#]T = the carrier of T by TOPS_1:15;
  hence p in Int [#]T;
end;
