On the extreme behaviour of $g_1(x,Q^2)$ at $x\to 0$
  On the basis of the U-matrix form of s-channel unitarization, we consider constraints unitarity provides for the spin structure function $g_1(x,Q^2)$ at $x\to 0$. Corresponding constraint for the spin structure function $h_1(x, Q^2)$ is given along. 
Sergey M. Troshin