reserve A for Tolerance_Space,
  X, Y for Subset of A;
reserve A for Approximation_Space,
  X for Subset of A;
reserve A for finite Tolerance_Space,
  X for Subset of A,
  x for Element of A;

theorem
  MemberFunc (X, A).x in [. 0, 1 .]
proof
  0 <= MemberFunc (X, A).x & MemberFunc (X, A).x <= 1 by Th38;
  hence thesis by XXREAL_1:1;
end;
