This paper considers the equivalence problem for quasi-cyclic codes over finite fields. The results obtained are used to construct isodual quasi-cyclic codes.

an ideal i of a ring r is called right baer-ideal if there exists an idempotent e 2 r such that r(i) = er. we know that r is quasi-baer if every ideal of r is a right baer-ideal, r is n-generalized right quasi-baer if for each i e r the ideal in is right baer-ideal, and r is right principaly quasi-baer if every principal right ideal of r is a right baer-ideal. therefore the concept of baer idea...

We present the package SADE (Symmetry Analysis of Differential Equations) for the determination of symmetries and related properties of systems of differential equations. The main methods implemented are: Lie, non classical, Lie-Bäcklund and potential symmetries, invariant solutions, first-integrals, Nöther theorem for both discrete and continuous systems, solution of ordinary differential equa...

We prove that whenever G is negatively curved and ? = G ZZ n acts geometrically on two CAT(0)-spaces X and X 0 , their visual boundaries are ?-equivariantly homeomorphic, answering aarmatively a question of Gromov in this special case. However, we give a simple example that shows that the natural ?-equivariant quasi-isometry from X to X 0 does not continuously extend to a homeomorphism of visua...

We consider quasi-perfect codes in Z over the `p metric, 2 ≤ p <∞. Through a computational approach, we determine all radii for which there are linear quasi-perfect codes for p = 2 and n = 2, 3. Moreover, we study codes with a certain degree of imperfection, a notion that generalizes the quasi-perfect codes. Numerical results concerning the codes with the smallest degree of imperfection are pre...

We consider the class of constant depth AND/OR circuits augmented with a layer of modular counting gates at the bottom layer, i.e AC◦MODm circuits. We show that the following holds for several types of gates G: by adding a gate of type G at the output, it is possible to obtain an equivalent probabilistic depth 2 circuit of quasipolynomial size consisting of a gate of type G at the output and a ...