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

theorem Th64:
  [0,1] in IBB
proof
A1: 1 >= 1 - 2 * 0 & 1 >= 2 * 0 - 1;
  0 is Point of I[01] & 1 is Point of I[01] by BORSUK_1:43;
  hence thesis by A1,Def9;
end;
