Kaplansky's second test problem in operator algebras

Chunlan Jiang, Minghui Ma, Rui Shi +1

Kaplansky's second test problem on similarity asks: if $T$ and $S$ are elements in a unital Banach algebra $\mathcal{B}$ and $T\oplus T$ is similar to $S\oplus S$ in $\mathbb{M}_2(…