This paper answers two questions proposed in [Fuzhen Zhang, Linear Algebra
Appl. 251 (1997) 21-57], showing that there exists a 2 x 2 quaternion matri
x with only two non-similar left eigenvalues that is not diagonalizable, an
d giving some necessary and sufficient conditions for
\A/-B B/A\ = 0
(C) 2000 Elsevier Science Inc. All rights reserved. AMS classification: 15A
33.