`vars'
------

vars(OBJ)
     :: A list of variables (indeterminates) in an expression OBJ.

RETURN
     list

OBJ
     arbitrary

   * Returns a list of variables (indeterminates) contained in a given
     expression.

   * Lists variables according to the variable ordering.

     [0] vars(x^2+y^2+a^2);
     [x,y,a]
     [1] vars(3/abc+2*xy/efg);
     [abc,xy,efg]
     [2] vars([x,y,z]);
     [x,y,z]

References
     *Note `var': var, *Note `uc': uc, *Note `ord': ord.

