Weak hands cannot be planted, meager skills have no foundation. Shallow wisdom is futile, how can one hope for a good name?扰扰从役倦，屑屑身事微。少壮轻年月，迟暮惜光辉。
YplusX = $YplusX;
if ($YminusX === null) {
$YminusX = new ParagonIE_Sodium_Core_Curve25519_Fe();
}
if (!($YminusX instanceof ParagonIE_Sodium_Core_Curve25519_Fe)) {
throw new TypeError('Argument 2 must be an instance of ParagonIE_Sodium_Core_Curve25519_Fe');
}
$this->YminusX = $YminusX;
if ($Z === null) {