Ruskai, M.B. Werner, E.
A Pair of Optimal Inequalities Related to the Error Function
(8K, LATeX 2e)

ABSTRACT.  We show that
$g_{\pi}(x) \leq \sqrt{\pi} e^{x^2} [1 - \hbox{erf}(x)] < g_4(x)$
where $g_k(x) = \frac{k}{(k-1)x + \sqrt{x^2+k}}$ 
and that these bounds are optimal for functions of this type.