                      Chebychev( x, {a0[0.1],a1[0.2],a2[-0.3]}))"
</pre>

<p>Create a <tt>RooAddPdf</tt> model of a <tt>RooGaussian</tt> and a <tt>RooChebychev</tt> (which
are implicitly named <tt>model_0</tt> and <tt>model_1</tt>), its observable <tt>x</tt> and its
parameters <tt>m,a0,a1,a2,Nsig</tt> and <tt>Nbkg</tt>

<p>Note that each object may be created only once (with [] or () brackets) but may be referenced multiple
times in the expression by just giving the name.  Here is a much more complicated ex