Decide Whether or Not the Transition Matrix Is Regular $\left[\begin{array}{ll}0.9 & 0.1 \\ 0.4 & 0.6\end{array}\right]$

Decide whether or not the transition matrix is regular.
- $\left[\begin{array}{ll}0.9 & 0.1 \\ 0.4 & 0.6\end{array}\right]$