On Mathias generic sets

Abstract

We present some results about generics for computable Mathias forcing. The $n$-generics and weak $n$-generics in this setting form a strict hierarchy as in the case of Cohen forcing. We analyze the complexity of the Mathias forcing relation, and show that if $G$ is any $n$-generic with $n\ge 3$ then it satisfies the jump property $G^{(n-1)}=G^{\prime }\oplus {\varnothing }^{(n)}$. We prove that every such $G$ has generalized high degree, and so cannot have even Cohen 1-generic degree. On the other hand, we show that $G$, together with any bi-immune set $A{\le }_T{\varnothing }^{(n-1)}$, computes a Cohen $n$-generic set.

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