Source: Notre Dame J. Formal Logic Volume 50, Number 4
(2009), 469-493.
Semi-hyperhypersimple c.e. sets, also known as diagonals, were introduced by
Kummer. He showed that by considering an analogue of hyperhypersimplicity, one
could characterize the sets which are the Halting problem relative to arbitrary
computable numberings. One could also consider half of splittings of maximal or
hyperhypersimple sets and get another variant of maximality and
hyperhypersimplicity, which are closely related to the study of automorphisms of
the c.e. sets. We investigate the Turing degrees of these classes of c.e. sets.
In particular, we show that the analogue of a theorem of Martin fails for these
classes.
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