Given a countable structure , we define the degree spectrum of to be the set of all enumeration degrees generated by the presentations of on the natural numbers. The co-spectrum of is the set of all lower bounds of . We prove some general properties of the degree spectra, which show that they behave with respect to their co-spectra very much like the cones of enumeration degrees. Among the results are the analogs of Selman's Theorem [14], the Minimal Pair Theorem and the existence of a quasi-minimal enumeration degree.
Soskov, I. (2004). DEGREE SPECTRA AND CO-SPECTRA OF STRUCTURES. Ann. Sofia Univ. Fac. Math. And Inf., 96, 45–68. Retrieved from https://annual.uni-sofia.bg/index.php/fmi/article/view/160