igcdex returns g = igcd(a, b), and optionally s and/or t such that

$\mathrm{igcdex}\left(2\,3\,'s'\,'t'\right)$

$1$

$s\;$$t$

$\mathrm{-1}$

$1$

$\mathrm{is}\left(2s+3t=1\right)$

$\mathrm{true}$