Î 11-conservation of combinatorial principles weaker than Ramsey's theorem for pairs

We study combinatorial principles weaker than Ramsey's theorem for pairs over the RCA0 (recursive comprehension axiom) system with Σ20-bounding. It is shown that the cohesiveness (COH), ascending and descending sequence (ADS), and chain/antichain (CAC) principles are all Π11-conservative over Σ20-bounding. In particular, none of these principles proves Σ20-induction.