diff --git a/src/014-slices/slices.go b/src/013-slices/slices.go
similarity index 100%
rename from src/014-slices/slices.go
rename to src/013-slices/slices.go
diff --git a/src/015-maps/maps.go b/src/014-maps/maps.go
similarity index 100%
rename from src/015-maps/maps.go
rename to src/014-maps/maps.go
diff --git a/src/015-maps/maps.sh b/src/014-maps/maps.sh
similarity index 100%
rename from src/015-maps/maps.sh
rename to src/014-maps/maps.sh
diff --git a/src/013-range/range.go b/src/015-range/range.go
similarity index 83%
rename from src/013-range/range.go
rename to src/015-range/range.go
index 1063513..b84f771 100644
--- a/src/013-range/range.go
+++ b/src/015-range/range.go
@@ -18,3 +18,6 @@ func main() {
     }
     fmt.Println(total / float64(len(x)))
 }
+
+// todo: comment on maps
+// todo: comment on channels
diff --git a/src/index.txt b/src/index.txt
index fcf3ad9..5b2d348 100644
--- a/src/index.txt
+++ b/src/index.txt
@@ -13,9 +13,9 @@ for
 if-else
 switch
 arrays
-range
 slices
 maps
+range
 functions
 multiple-return-values
 varadic-functions
diff --git a/tool/src/build-html.go b/tool/src/build-html.go
index 87428af..2644de9 100644
--- a/tool/src/build-html.go
+++ b/tool/src/build-html.go
@@ -41,7 +41,7 @@ func sha1Sum(s string) string {
 
 var cacheDir = "/tmp/gbe-book-cache"
 
-func mustReadFile(path string) {
+func mustReadFile(path string) string {
     bytes, err := ioutil.ReadFile(path)
     check(err)
     return string(bytes)