 - t) * ((-s2) + (1 - t) * (2 * (-s2) + (1 - t) * (8 - 
          12 * (-s2) + (1 - t) * (14 * (-s2) - 11 + (1 - t) * (4 - 
          5 * (-s2)))))) + t * ((-s1) + t * (2 * (-s1) + t * (8 - 
      12 * (-s1) + t * (14 * (-s1) - 11 + t * (4 - 5 * (-s1)))))) + 
      (t - 1) * ((-s2) + (t - 1) * (2 * (-s2) + (t - 1) * (t - 
          1) * (-2 * (-s2) - (t - 1) * (-s2)))))^2
</pre></div>
</div></div>
    <p>
    Again, a simple loop can be used to generate tangent expressions
    for all X-spline scenarios.
  