Nondensity of Double Bubbles in the D.C.E. Degrees
نویسندگان
چکیده
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.
منابع مشابه
The nonisolating degrees are nowhere dense in the computably enumerable degrees
The d.c.e. degrees were first studied by Cooper [5] and Lachlan who showed that there is a proper d.c.e degree, a d.c.e. degree containing no c.e. sets, and that every nonzero d.c.e. degree bounds a nonzero c.e. degree, respectively. The main motivation of research on the d.c.e. degrees is to study the differences between the structures of d.c.e. degrees and Δ2 degrees, and between the structur...
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