double curly brackets

    
      
diff --git a/notes-en/ncd.md b/notes-en/ncd.md
index c82e83e..84b0193 100644
--- a/notes-en/ncd.md
+++ b/notes-en/ncd.md
@@ -3,7 +3,7 @@
 
 ## Calculation
 
-$$NCD_{Z}(x,y)={\frac  {Z(xy)-\min\{Z(x),Z(y)\}}{\max\{Z(x),Z(y)\}}}.$$
+$$NCD_{Z}(x,y)={\frac  {Z(xy)-\min\\{Z(x),Z(y)\\}}{\max\\{Z(x),Z(y)\\}}}.$$
 
 ## Normal Compressor