Complex sentence: These probabilities form "a priori" a probability distribution for the observation, which Ray Solomonoff proved to be machine-invariant (called the invariance theorem) and can be used with Bayes' theorem to predict the most likely continuation of that observation.
Split into simpler sentences: These probabilities form "a priori" a probability distribution for the observation, which Ray Solomonoff proved to be machine-invariant (called the invariance theorem). Thus it can be used with Bayes' theorem to predict the most likely continuation of that observation.