`coef'
------

coef(POLY,DEG[,VAR])
     :: The coefficient of a polynomial POLY at degree DEG with respect
     to the variable VAR (main variable if unspecified).

RETURN
     polynomial

POLY
     polynomial

VAR
     indeterminate

DEG
     non-negative integer

   * The coefficient of a polynomial POLY at degree DEG with respect to
     the variable VAR.

   * The default value for VAR is the main variable, i.e., var(POLY).

   * For multi-variate polynomials, access to coefficients depends on
     the specified indeterminates.  For example, taking coef for the
     main variable is much faster than for other variables.

     [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

References
     *Note `var': var, *Note `deg mindeg': deg mindeg.

