`coef'
------

coef(POLY,DEG[,VAR])
     :: POLY $B$N(B VAR ($B>JN,;~$O<gJQ?t(B) $B$K4X$9$k(B DEG $B<!$N78?t(B.

RETURN
     $BB?9`<0(B

POLY
     $BB?9`<0(B

VAR
     $BITDj85(B

DEG
     $B<+A3?t(B

   * POLY $B$N(B VAR $B$K4X$9$k(B DEG $B<!$N78?t$r=PNO$9$k(B.

   * VAR $B$O(B, $B>JN,$9$k$H<gJQ?t(B var(POLY) $B$@$H$_$J$5$l$k(B.

   * VAR $B$,<gJQ?t$G$J$$;~(B, VAR $B$,<gJQ?t$N>l9g$KHf3S$7$F(B $B8zN($,Mn$A$k(B.

     [0] A = (x+y+z)^3;
     x^3+(3*y+3*z)*x^2+(3*y^2+6*z*y+3*z^2)*x+y^3+3*z*y^2+3*z^2*y+z^3
     [1] coef(A,1,y);
     3*x^2+6*z*x+3*z^2
     [2] coef(A,0);
     y^3+3*z*y^2+3*z^2*y+z^3

$B;2>H(B
     *Note `var': var, *Note `deg mindeg': deg mindeg.

