No Arabic abstract
A hypergroup is stringent if $a boxplus b$ is a singleton whenever $a eq -b$. A hyperfield is stringent if the underlying additive hypergroup is. Every doubly distributive skew hyperfield is stringent, but not vice versa. We present a classification of stringent hypergroups, from which a classification of doubly distributive skew hyperfields follows. It follows from our classification that every such hyperfield is a quotient of a skew field.
The noncommutative projective scheme $operatorname{mathsf{Proj_{nc}}} S$ of a $(pm 1)$-skew polynomial algebra $S$ in $n$ variables is considered to be a $(pm 1)$-skew projective space of dimension $n-1$. In this paper, using combinatorial methods, we give a classification theorem for $(pm 1)$-skew projective spaces. Specifically, among other equivalences, we prove that $(pm 1)$-skew projective spaces $operatorname{mathsf{Proj_{nc}}} S$ and $operatorname{mathsf{Proj_{nc}}} S$ are isomorphic if and only if certain graphs associated to $S$ and $S$ are switching (or mutation) equivalent. We also discuss invariants of $(pm 1)$-skew projective spaces from a combinatorial point of view.
A finite semifield $D$ is a finite nonassociative ring with identity such that the set $D^*=Dsetminus{0}$ is closed under the product. In this paper we obtain a computer-assisted description of all 64-element finite semifields, which completes the classification of finite semifields of order 125 or less.
We prove simplicity, and compute $delta$-derivations and symmetric associative forms of algebras in the title.
We determine the skew fields of fractions of the enveloping algebra of the Lie superalgebra osp(1, 2) and of some significant subsu-peralgebras of the Lie superalgebra osp(1, 4). We compare the kinds of skew fields arising from this super context with the Weyl skew fields in the classical Gelfand-Kirillov property.
We study prime ideals in skew power series rings $T:=R[[y;tau,delta]]$, for suitably conditioned right noetherian complete semilocal rings $R$, automorphisms $tau$ of $R$, and $tau$-derivations $delta$ of $R$. These rings were introduced by Venjakob, motivated by issues in noncommutative Iwasawa theory. Our main results concern Cutting Down and Lying Over. In particular, under the additional assumption that $delta = tau - id$ (a basic feature of the Iwasawa-theoretic context), we prove: If $I$ is an ideal of $R$, then there exists a prime ideal $P$ of $S$ contracting to $I$ if and only if $I$ is a $delta$-stable $tau$-prime ideal of $R$. Our approach essentially depends on two key ingredients: First, the algebras considered are zariskian (in the sense of Li and Van Oystaeyen), and so the ideals are all topologically closed. Second, topological arguments can be used to apply previous results of Goodearl and the author on skew polynomial rings.