Nondensity of double bubbles in the D.C.E. degrees

Abstract

© Springer International Publishing AG 2017.In this paper, we show that the so-called “double bubbles” are not downward dense in the d.c.e. degrees. Here, a pair of d.c.e. degrees d1 > d2 > 0 forms a double bubble if all d.c.e. degrees below d1 are comparable with d2.