 to their trigonometric equivalents.</dd>
 <dt><b><tt>denom(a)</tt></b></dt>
	<dd> Gives the denominator of <tt>a</tt>.</dd>
 <dt><b><tt>depends(a,b)</tt></b></dt>
	<dd> Declares <tt>a</tt> to be a function of <tt>
    b</tt>.  This is useful for writing unevaluated derivatives, as in
  specifying differential equations.</dd>
 <dt><b><tt>desolve(a,b)</tt></b></dt>
	<dd> Attempts to solve a linear system <tt>a</tt> of
  ODE's for unknowns <tt>b</tt> using Laplace transforms.</dd>
 <dt><b><tt>determinant(a)</