`dp_dtop'
---------

dp_dtop(DPOLY,VLIST)
     ::

RETURN
     ¿༰
DPOLY
     ʬɽ¿༰
VLIST
     ꥹ

   * ʬɽ¿༰, Ϳ줿긵ꥹȤѤ¿༰Ѵ.
   * 긵ꥹȤ, Ĺʬɽ¿༰ѿθĿȰפƤв
     Ǥ褤.

     [53] T=dp_ptod((x+y+z)^2,[x,y]);
     (1)*<<2,0>>+(2)*<<1,1>>+(1)*<<0,2>>+(2*z)*<<1,0>>+(2*z)*<<0,1>>+(z^2)*<<0,0>>
     [54] P=dp_dtop(T,[a,b]);
     z^2+(2*a+2*b)*z+a^2+2*b*a+b^2

