Remarks on the Additional Symmetries and W-Constraints in the   Generalized KdV Hierarchy
  Additional symmetries of the $p$-reduced KP hierarchy are generated by the Lax operator $L$ and another operator $M$, satisfying $res (M^n L^{m+n/p})$ = 0 for $1 \leq n \leq p-1$ and $m \geq -1$ with the condition that ${\partial L \over {\partial t_{kp}}}$ = 0, $k$ = 1, 2,..... We show explicitly that the generators of these additional symmetries satisfy a closed and consistent W-algebra only when we impose the extra condition that ${\partial M \over {\partial t_{kp}}} = 0$. 
Sudhakar Panda and Shibaji Roy