Heredity for triangular operators

Resumo

A proof is given that if the lower triangular infinite matrix $T$ acts boundedly on $\ell^2$ and U is the unilateral shift, the sequence $(U^*)^nTU^n$ inherits from $T$ the following properties: posinormality, dominance, $M$-hyponormality, hyponormality, normality, compactness, and noncompactness.  Also, it is demonstrated that the upper triangular matrix $T^*$ is dominant if and only if $T$ is a diagonal matrix.