Geodesic
$\Delta_2^0$-Copies of Linear Orderings
Algebra i logika, Tome 45 (2006) no. 3, pp. 354-370

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It is proved that, for any $n\in\omega$, there exist countable linear orderings $L_n$ whose $\Delta_2^0$-spectrum consists of exactly all non $n$-low $\Delta_2^0$-degrees. Properties of such orderings are examined, for $n=1$ and $n=2$.
Keywords: countable linear ordering, $\Delta_2^0$-degree, $\Delta_2^0$-spectrum. 
@article{AL_2006_45_3_a3,
     author = {A. N. Frolov},
     title = {$\Delta_2^0${-Copies} of {Linear} {Orderings}},
     journal = {Algebra i logika},
     pages = {354--370},
     publisher = {mathdoc},
     volume = {45},
     number = {3},
     year = {2006},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/AL_2006_45_3_a3/}
}
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A. N. Frolov. $\Delta_2^0$-Copies of Linear Orderings. Algebra i logika, Tome 45 (2006) no. 3, pp. 354-370. http://geodesic.mathdoc.fr/item/AL_2006_45_3_a3/