Effective Randomness of Unions and Intersections

We investigate the μ-randomness of unions and intersections of random sets under various notions of randomness corresponding to different probability measures. For example, the union of two relatively Martin-Löf random sets is not Martin-Löf random but is random with respect to the Bernoulli measure $\lambda_{\frac{3}{4}}$ under which any number belongs to the set with probability $\frac{3}{4}$. Conversely, any $\lambda_{\frac{3}{4}}$ random set is the union of two Martin-Löf random sets. Unions and intersections of random closed sets are also studied.