  In the context of relativistic quantum mechanics, where the Schr\"odinger
equation is replaced by the spinless Salpeter equation, we show how to
construct a large class of upper limits on the critical value,
$g_{\rm{c}}^{(\ell)}$, of the coupling constant, $g$, of the central potential,
$V(r)=-g v(r)$. This critical value is the value of $g$ for which a first
$\ell$-wave bound state appears.
