Density of Recursively Inseparable R. E. Sets and Universal Recrusively Inseparability

(整期优先)网络出版时间:1986-04-14
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Problemsaboutdensityareremarkableinthetheoryofdegreesofunsolvability.Owingtotheirdifficultyfewresultshavebeenobtainedtillnow.Sacks1964showedthatther.e.degreesaredense;Fejer1980showedthatnonbrachingdegreesaredenseinther.e.degrees,thisisthefirstnontrivialdefinablesubsetofthedegreesknowntobedense.