Two More Characterizations of K-Triviality
Noam Greenberg, Joseph S. Miller, Benoit Monin, Daniel D. Turetsky · Notre Dame Journal of Formal Logic · 2018
We give two new characterizations of K-triviality. We show that if for all Y such that Ω is Y-random, Ω is (Y⊕A)-random, then A is K-trivial. The other direction was proved by Stephan and Yu, giving us the first titular characterization of K-triviality and answering a question of Yu. We also prove that if A is K-trivial, then for all Y such that Ω is Y-random, (Y⊕A)≡LRY. This answers a question of Merkle and Yu. The other direction is immediate, so we have the second characterization of K-triviality. The proof of the first characterization uses a new cupping result. We prove that if A≰LRB, then for every set X there is a B-random set Y such that X is computable from Y⊕A.