Partially isometric truncated and dual truncated Toeplitz operators

Abstract

Let $θ$ be a non-constant inner function and let $ϕ=\overline{u}v$, where $u$ and $v$ are inner functions such that $v$ divides $θ$. In this paper we characterize the partially isometric truncated Toeplitz operators $A_ϕ$ and dual truncated Toeplitz operators $D_ϕ$ with symbols of the form $ϕ=\overline{u}v$. Along with that, we obtain a few more characterization results, including the space of extremal vectors for non-zero partially isometric truncated and dual truncated Toeplitz operators.