diff --git a/docs/errata.md b/docs/errata.md
index e0330ce..8b18b44 100644
--- a/docs/errata.md
+++ b/docs/errata.md
@@ -17,3 +17,18 @@ G_8=r_9+\gamma G_9=-1+0.6 \times(-2.176)=-2.3056 \approx-2.3
 \end{array}
 $$
 
+* 149页，式(6.15) 改为
+
+$$
+\begin{aligned}
+V^{\pi}(s) &\le Q^{\pi}(s,\pi'(s)) \\
+&=E\left[r_{t}+V^{\pi}\left(s_{t+1}\right) | s_{t}=s, a_{t}=\pi^{\prime}\left(s_{t}\right)\right]\\
+&\le E\left[r_{t}+Q^{\pi}\left(s_{t+1}, \pi^{\prime}\left(s_{t+1}\right)\right) | s_{t}=s, a_{t}=\pi^{\prime}\left(s_{t}\right)\right] \\
+&=E\left[r_{t}+r_{t+1}+V^{\pi}\left(s_{t+2}\right) |s_{t}=s, a_{t}=\pi^{\prime}\left(s_{t}\right)\right]  \\
+& \le E\left[r_{t}+r_{t+1}+Q^{\pi}\left(s_{t+2},\pi'(s_{t+2}\right) | s_{t}=s, a_{t}=\pi^{\prime}\left(s_{t}\right)\right] \\
+& = E\left[r_{t}+r_{t+1}+r_{t+2}+V^{\pi}\left(s_{t+3}\right) |s_{t}=s, a_{t}=\pi^{\prime}\left(s_{t}\right)\right] \\
+& \le \cdots\\
+& \le E\left[r_{t}+r_{t+1}+r_{t+2}+\cdots | s_{t}=s, a_{t}=\pi^{\prime}\left(s_{t}\right)\right]  \\
+& = V^{\pi'}(s)
+\end{aligned}
+$$