The equational theory of the Weihrauch lattice with multiplication

Abstract

We study the equational theory of the Weihrauch lattice with multiplication, meaning the collection of equations between terms built from variables, the lattice operations $\bigsqcup$, $\sqcap$, the product $\times$, and the finite parallelization $(-{)}^{\ast }$ which are true however we substitute Weihrauch degrees for the variables. We provide a combinatorial description of these in terms of a reducibility between finite graphs, and moreover, show that deciding which equations are true in this sense is complete for the third level of the polynomial hierarchy.

Proposition 4 was false in v1; removed it and added a related relative completeness result (Theorem 15). See the erratum in the document