It's actually easily provable, and simply by observation, because "smaller things combining" has a much simpler definition than what you're assuming! What it actually refers to is how some spaceships, such as the Waterbear -- https://www.youtube.com/watch?v=on3ZLLKQp-4 -- are constructed explicitly as a circuit of building blocks (as you can see in the video), whereas elementary spaceships like this knightship consist of "space dust" that isn't separable into independently-functioning components.