  In a recent paper Zhang and Li have doubted our claim that whenever a
nonlinear equation has solutions in terms of the Jacobi elliptic functions
$\cn(x,m)$ and $\dn(x,m)$, then the same nonlinear equation will necessarily
also have solutions in terms of $\dn(x,m) \pm \sqrt{m} \cn(x,m)$. We point out
the flaw in their argument and show why our assertion is indeed valid.
