diff --git a/content/substrate/intro/slides.md b/content/substrate/intro/slides.md
index 14d64de..56a0f9e 100644
--- a/content/substrate/intro/slides.md
+++ b/content/substrate/intro/slides.md
@@ -488,7 +488,7 @@ associated with each block.
 
 ### State Transition Function
 
-$$STF = F(block_{N}, state_{N}, code_{N}): state_{N+1}$$
+$$STF = F(block_{N+1}, state_{N}, code_{N}): state_{N+1}$$
 
 ---v