Summary
Answering a question of Per Lindström, we show that there is no “plus-capping” degree, i.e. that for any incomplete r.e. degreew, there is an incomplete r.e. degreea>w such that there is no r.e. degreev>w witha∩v=w.
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Mathematics subject classification: 03D30
The authors would like to thank Per Lindström for raising the question and Carl Jockusch for communicating it to them. The first author was partially supported by a U.S./New Zealand binational grant. The second author was partially supported by NSF grant DMS-9100114 and the U.S./New Zealand binational NSF grant INT-9020558
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Downey, R.G., Lempp, S. There is no plus-capping degree. Arch Math Logic 33, 109–119 (1994). https://doi.org/10.1007/BF01352932
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DOI: https://doi.org/10.1007/BF01352932