On the additive theory of prime numbers II

The undecidability of the additive theory of primes (with identity) as well as the theory Th(N,+, n -> p\_n), where p\_n denotes the (n+1)-th prime, are open questions. As a possible approach, we extend the latter theory by adding some extra function. In this direction we show the undecidability of the existential part of the theory Th(N, +, n -> p\_n, n -> r\_n), where r\_n is the remainder of p\_n divided by n in the euclidian division

Strict pseudocontractions and demicontractions, their properties and applications

We give properties of strict pseudocontractions and demicontractions defined on a Hilbert space, which constitute wide classes of operators that arise in iterative methods for solving fixed point problems. In particular, we give necessary and sufficient conditions under which a convex combination and composition of strict pseudocontractions as well as demicontractions that share a common fixed point is again a strict pseudocontraction or a demicontraction, respectively. Moreover, we introduce a generalized relaxation of composition of demicontraction and give its properties. We apply these properties to prove the weak convergence of a class of algorithms that is wider than the Douglas-Rachford algorithm and projected Landweber algorithms. We have also presented two numerical examples, where we compare the behavior of the presented methods with the Douglas-Rachford method.Comment: 27 pages, 3 figure

Tree inclusions in windows and slices

$P$ is an embedded subtree of $T$ if $P$ can be obtained by deleting some nodes from $T$: if a node $v$ is deleted, all edges adjacent to $v$ are also deleted, and outgoing edges are replaced by edges going from the parent of $v$ (if it exists) to the children of $v$. Deciding whether $P$ is an embedded subtree of $T$ is known to be NP-complete. Given two trees (a target $T$ and a pattern $P$) and a natural number $w$, we address two problems: 1. counting the number of windows of $T$ having height exactly $w$ and containing pattern $P$ as an embedded subtree, and 2. counting the number of slices of $T$ having height exactly $w$ and containing pattern $P$ as an embedded subtree