diff --git a/README.md b/README.md
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--- a/README.md
+++ b/README.md
@@ -4,7 +4,7 @@
 
 It's a simple minimal lisp interpreter written in ruby.
 
-![](./screenshot/demo.svg)
+![](./screenshot/demo.png)
 
 ### Feature
 
@@ -15,4 +15,8 @@ It's a simple minimal lisp interpreter written in ruby.
 
 ```bash
 $ ruby ./prol.rb
-```
\ No newline at end of file
+```
+
+### Acknowledgement
+
+[Tesla I. Zhang](https://github.com/ice1000), for pointing out errors and patient guidance
\ No newline at end of file
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