Given world A and wirld B are both determined, then you could have a Laplace Demon model each world on a mathematical function.

The union of those functions would just be another function. A piecewise one, sure, but a function all the same. Or at the very least, it wouldn't necessarily not be such a function. It is possie to combine two worlds and have them still be determined.

Ooh, here's an easy proof. Suppose world zb, by coincidence, just haooens ro be exactly equivalent to the domain of A that it is slipping into. A therefore does not change by the introduction of B. Therefore, if A was determined before, the the union of A + B must also be determined, thus violating the iff conditioned premise 1b.