diff --git a/Probability.md b/Probability.md
index 9f938eb..d39feea 100644
--- a/Probability.md
+++ b/Probability.md
@@ -58,4 +58,6 @@
 
     ![](https://latex.codecogs.com/gif.latex?(x+y)^{n}&space;=&space;\sum_{k=0}^{n}\binom{n}{k}x^{k}y^{n-k})
 
-*
+* **Proposition 4.4**
+
+    ![](https://latex.codecogs.com/gif.latex?P(\bigcup_{1}^{n}E_{i})&space;=&space;\sum_{1}^{n}P(E_{i})-\sum_{i_{1}%3Ci_{2}}P(E_{i_{1}}E_{i_{2}})+...&space;+(-1)^{r+1}\sum_{i_{1}%3Ci_{2}%3C...%3Ci_{r}}P(E_{i_{1}}E_{i_2}...E_{i_{r}})+...+(-1)^{n+1}P(E_{i_{1}}E_{i_{2}}...E_{i_{n}}))))