diff --git a/ch04.asciidoc b/ch04.asciidoc
index 0be6636a..36fac9fc 100644
--- a/ch04.asciidoc
+++ b/ch04.asciidoc
@@ -353,7 +353,7 @@ Address: 1PRTTaJesdNovgne6Ehcdu1fpEdX7913CK
 
 ==== Key Formats
 
-Both private and public keys can be represented in a number of different formats. These representations all encode the same number, even though they look different. These formats are primarily used to make it easy for people to read and transcribe keys without introducing errors.
+((("keys and addresses", "bitcoin addresses", "key formats")))Both private and public keys can be represented in a number of different formats. These representations all encode the same number, even though they look different. These formats are primarily used to make it easy for people to read and transcribe keys without introducing errors.
 
 [[priv_formats]]
 ===== Private key formats