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diff --git a/xx-elapsed.go b/048-elapsed.go
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diff --git a/xx-email.go b/049-email.go
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diff --git a/xx-tcp-client.go b/089-tcp-client.go
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diff --git a/xx-tcp-server.go b/090-tcp-server.go
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diff --git a/xx-tickers.go b/091-tickers.go
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diff --git a/xx-time.go b/092-time.go
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diff --git a/xx-timers.go b/093-timers.go
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diff --git a/xx-url.go b/094-url.go
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diff --git a/xx-users.go b/095-users.go
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diff --git a/xx-worker-pool.go b/096-worker-pool.go
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diff --git a/tool/renumber.go b/tool/renumber.go
index f5e7071..2b6ac10 100644
--- a/tool/renumber.go
+++ b/tool/renumber.go
@@ -8,6 +8,7 @@ import (
     "io/ioutil"
     "strings"
     "regexp"
+    "os"
 )
 
 func main() {
@@ -38,7 +39,7 @@ func main() {
     // rename some stuff
     for index, indexName := range indexNames {
         oldName := sourceMap[indexName]
-        newName := fmt.Sprintf("%d-%s.go", index+1, indexName)
+        newName := fmt.Sprintf("%03d-%s.go", index+1, indexName)
         os.Rename(oldName, newName)
     }
 }