Wadge-like degrees of Borel bqo-valued functions

Abstract:

We unite two well known generalisations of the Wadge theory. The first one considers more general reducing functions than the continuous functions in the classical case, and the second one extends Wadge reducibility from sets (i.e., $\{0,1\}$-valued functions) to $Q$-valued functions, for a better quasiorder $Q$. In this article, we consider more general reducibilities on the $Q$-valued functions and generalise some results of L. Motto Ros [J. Symbolic Logic 74 (2009), pp. 27–49] in the first direction and of T. Kihara and A. Montalbán [Trans. Amer. Math. Soc. 370 (2018), pp. 9025–9044] in the second direction: Our main result states that the structure of the $\mathbf {\Delta }^0_\alpha$-degrees of $\mathbf {\Delta }^0_{\alpha +\gamma }$-measurable $Q$-valued functions is isomorphic to the $\mathbf {\Delta }^0_\beta$-degrees of $\mathbf {\Delta }^0_{\beta +\gamma }$-measurable $Q$-valued functions, and these are isomorphic to the generalized homomorphism order on the $\gamma$-th iterated $Q$-labeled forests.