A Nonlow2 C.e. Degree Which Bounds No Diamond Bases
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چکیده
A computably enumerable (c.e.) Turing degree is a diamond base if and only if it is the bottom of a diamond of c.e. degrees with top 0′. Cooper and Li [3] showed that no low2 c.e. degree can bound a diamond bases. In the present paper, we show that there exists a nonlow2 c.e. degree which does not bound a diamond base. Thus, we refute an attractive natural attempt to define the jump class low2.
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تاریخ انتشار 2001