Mixed quasi-\'etale quotients with arbitrary singularities

A mixed quasi-etale quotient is the quotient of the product of a curve of genus at least 2 with itself by the action of a group which exchanges the two factors and acts freely outside a finite subset. A mixed quasi-etale surface is the minimal resolution of its singularities. We produce an algorithm computing all mixed quasi-etale surfaces with given geometric genus, irregularity and self-intersection of the canonical class. We prove that all irregular mixed quasi-etale surfaces of general type are minimal. As an application, we classify all irregular mixed quasi-etale surfaces of general type with genus equal to the irregularity, and all the regular ones with K-2 > 0, thus constructing new examples of surfaces of general type with chi = 1. We mention the first example of a minimal surface of general type with p(g) = q = 1 and Albanese fibre of genus bigger than K-2.