We consider the semigroup Ext(A, B) of extensions of a separable C *-algebra A by a stable C *-algebra B modulo unitary equivalence and modulo asymptotically split extensions. This semigroup contains the group Ext −1/2 (A, B) of invertible elements (i.e. of semi-invertible extensions). We show that the functor Ext 1/2 (A, B) is homotopy invariant and that it coincides with the functor of homoto...

We extend the Larson–Sweedler theorem [10] to weak Hopf algebras by proving that a finite dimensional weak bialgebra is a weak Hopf algebra iff it possesses a non-degenerate left integral. We show that the category of modules over a weak Hopf algebra is autonomous monoidal with semisimple unit and invertible modules. We also reveal the connection of invertible modules to left and right grouplik...

In this paper, we describe non invertible matrix in GF(2) which can be used as multiplication matrix in Hill Cipher technique for one way hash algorithm. The matrices proposed are permutation matrices with exactly one entry 1 in each row and each column and 0 elsewhere. Such matrices represent a permutation of m elements. Since the invention, Hill cipher algorithm was used for symmetric encrypt...

For a ring R, we denote by R[L] the free R-module spanned by the isotopy classes of singular links in S. Given two invertible elements x, t ∈ R, the HOMFLY-PT skein module of singular links in S (relative to the triple (R, t, x)) is the quotient of R[L] by local relations, called skein relations, that involve t and x. We compute the HOMFLY-PT skein module of singular links for any R such that (...

1. Let A be an n× n matrix with complex coefficients. Define trA to be the sum of the diagonal elements. Show that trA is invariant under conjugation, i.e., trA = trPAP for all invertible n× n matrices P. Proof. Let P be an invertible matrix. Let ~pk be the k-th row of P, ~qj the j-th column of P, and ~ ai the i-th column of A. The k-th row of the matrix PA is 〈~pk · ~ a1, . . . ,~pk · ~ an〉. S...

Let K be a general nite commutative ring. We refer to a family gn, n = 1, 2, . . . of bijective polynomial multivariate maps of K as a family with invertible decomposition gn = g ng 2 n . . . g k n, such that the knowledge of the composition of g n allows computation of g i n for O(n ) (s > 0) elementary steps. A polynomial map g is stable if all non-identical elements of kind g, t > 0 are of t...

We consider a family of finitely presented groups, called Universal Left Invertible Element (or ULIE) groups, that are universal for existence of one–sided invertible elements in a group ring K[G], where K is a field or a division ring. We show that for testing Kaplansky’s Direct Finiteness Conjecture, it suffices to test it on ULIE groups, and we show that there is an infinite family of non-am...

If (fn) is a sequence of elements of an infinite dimensional Hilbert space H and (en) is an orthonormal basis for H , we define the preframe operator T : H → H by: Ten = fn. It follows that for any f ∈ H , T ∗f = ∑ n〈f, fn〉en. Hence, (fn) is a frame if and only if T ∗ is an isomorphism (called the frame transform) and in this case S = TT ∗ is an invertible operator on H called the frame operato...

For two central Drazin invertible elements a and b of ring, we first prove that + is under the condition ab = 0. Then establish relation between invertibility 1 acb, when a2b aba b2a bab hold, also ba valid. When are group elements, additive properties inverses studied abbc baac.