reserve T for non empty TopSpace,
  a, b, c, d for Point of T;

theorem Th67:
  [1/2,0] in IBB
proof
A1: 0 <= 1 - 2 * (1/2);
  1/2 is Point of I[01] & 0 is Point of I[01] by BORSUK_1:43;
  hence thesis by A1,Def9;
end;
