How to multiply `material.opacityNode`, not replace it?

[PavelBoytchev]

The opacity property of the material is materialOpacity:

import {..., materialOpacity} from 'three/tsl';
:
material.opacityNode = Fn(() => {
    const alphaFactor = Const(0.5)
    return materialOpacity.mul(alphaFactor);
})()