Recently Zuhair Abdul Ghafoor Al-Johar [12] has directed our attention to a syntactic constraint that is—on the face of it—tighter than NF’s device of stratification; in this little essay I consider a weakening, namely the generalisation of stratification to stratification mod n. So far the coterie of NFistes has considered neither the possibility that the class of unstratified formulæ in the l...

An (I,Fd)-partition of a graph is a partition of the vertices of the graph into two sets I and F , such that I is an independent set and F induces a forest of maximum degree at most d. We show that for all M < 3 and d ≥ 2 3−M − 2, if a graph has maximum average degree less than M , then it has an (I,Fd)-partition. Additionally, we prove that for all 8 3 ≤ M < 3 and d ≥ 1 3−M , if a graph has ma...

We consider the Turing degrees of prime models of complete decidable theories. In particular we show that every complete decidable atomic theory has a prime model whose elementary diagram is low. We combine the construction used in the proof with other constructions to show that complete decidable atomic theories have low prime models with added properties. If we have a complete decidable atomi...

There are many functions of the degree sequence of a graph which give lower bounds on the independence number of the graph. In particular, for every graph G, α(G) ≥ R(d(G)), where R is the residue of the degree sequence of G. We consider the precision of this estimate when it is applied to semi-regular degree sequences. We show that the residue nearly always gives the best possible estimate on ...

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 hyperhypersimplic...

The purpose of this paper is to prove that, with the exception of C 4 , there are no graphs of diameter 2 and maximum degree d with d 2 vertices . On one hand our paper is an extension of [4] where it was proved that there are at most four Moore graphs of diameter 2 (i .e . graphs of diameter 2, maximum degree d, and d2 + 1 vertices) . We also use the eigenvalue method developed in that paper ....

We survey what is known about limitwise monotonic functions and sets and discuss their applications in effective algebra and computable model theory. Additionally, we characterize the computably enumerable degrees that are totally limitwise monotonic, show the support strictly increasing 0′-limitwise monotonic sets on Q do not capture the sets with computable strong η-representations, and study...

We investigate the complexity of several classical model theoretic theorems about prime and atomic models and omitting types. Some are provable in RCA0, and others are equivalent to ACA0. One, that every atomic theory has an atomic model, is not provable in RCA0 but is incomparable with WKL0, more than Π1 conservative over RCA0 and strictly weaker than all the combinatorial principles of Hirsch...