The Major Subdegree Problem of A. H. Lachlan (first posed in 1967) has become the longest-standing open question concerning the structure of the computably enumerable (c.e.) degrees. A c.e. degree a is a major subdegree of a c.e. degree b > a if for any c.e. degree x, 0′ = b ∨ x if and only if 0′ = a ∨ x. In this paper, we show that every c.e. degree b 6= 0 or 0′ has a major subdegree, answerin...

in this research the degree to which search abilities have been inserted into the search engines of persian and non-persian e-journals has been investigated. 97 persian e-journals (pej) and 30 non-persian, in this case english, e-journals (eej) represent the research population. the required data were gathered through designing a checklist, which was filled out for each pej and eej. the results...

Recent empirical evaluations of exact algorithms for Feedback Vertex Set have demonstrated the efficiency a highest-degree branching algorithm with degree-based pruning. In this paper, we prove that empirically fast runs in $$O(3.460^k n)$$ time, where k is solution size. This improves previous best $$O(3.619^k -time deterministic obtained by Kociumaka and Pilipczuk (Inf Process Lett 114:556–56...