diff --git a/README.md b/README.md
index 1d6c93e..3275c20 100644
--- a/README.md
+++ b/README.md
@@ -33,11 +33,11 @@ PsyNet [^1]
 term
 : definition
 
-This is ==very== important
+This is <mark>very</mark> important
 
-H~2~0
+H<sub>2</sub>0
 
-X^2^
+X<sup>2</sup>
 
 ## TO DDO