diff --git a/066-line-filter/line-filter.go b/058-line-filter/line-filter.go
similarity index 100%
rename from 066-line-filter/line-filter.go
rename to 058-line-filter/line-filter.go
diff --git a/066-line-filter/line-filter.sh b/058-line-filter/line-filter.sh
similarity index 100%
rename from 066-line-filter/line-filter.sh
rename to 058-line-filter/line-filter.sh
diff --git a/058-command-line-arguments/command-line-arguments.go b/059-command-line-arguments/command-line-arguments.go
similarity index 100%
rename from 058-command-line-arguments/command-line-arguments.go
rename to 059-command-line-arguments/command-line-arguments.go
diff --git a/058-command-line-arguments/command-line-arguments.sh b/059-command-line-arguments/command-line-arguments.sh
similarity index 100%
rename from 058-command-line-arguments/command-line-arguments.sh
rename to 059-command-line-arguments/command-line-arguments.sh
diff --git a/059-command-line-flags/command-line-flags.go b/060-command-line-flags/command-line-flags.go
similarity index 100%
rename from 059-command-line-flags/command-line-flags.go
rename to 060-command-line-flags/command-line-flags.go
diff --git a/060-environment-variables/environment-variables.go b/061-environment-variables/environment-variables.go
similarity index 100%
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rename to 061-environment-variables/environment-variables.go
diff --git a/060-environment-variables/environment-variables.sh b/061-environment-variables/environment-variables.sh
similarity index 100%
rename from 060-environment-variables/environment-variables.sh
rename to 061-environment-variables/environment-variables.sh
diff --git a/061-spawning-processes/spawning-processes.go b/062-spawning-processes/spawning-processes.go
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rename from 061-spawning-processes/spawning-processes.go
rename to 062-spawning-processes/spawning-processes.go
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rename to 062-spawning-processes/spawning-processes.sh
diff --git a/062-execing-processes/execing-processes.go b/063-execing-processes/execing-processes.go
similarity index 100%
rename from 062-execing-processes/execing-processes.go
rename to 063-execing-processes/execing-processes.go
diff --git a/063-signals/signals.go b/064-signals/signals.go
similarity index 100%
rename from 063-signals/signals.go
rename to 064-signals/signals.go
diff --git a/063-signals/signals.sh b/064-signals/signals.sh
similarity index 100%
rename from 063-signals/signals.sh
rename to 064-signals/signals.sh
diff --git a/064-exit/exit.go b/065-exit/exit.go
similarity index 100%
rename from 064-exit/exit.go
rename to 065-exit/exit.go
diff --git a/064-exit/exit.sh b/065-exit/exit.sh
similarity index 100%
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rename to 065-exit/exit.sh
diff --git a/065-reading-input/reading-input.go b/065-reading-input/reading-input.go
deleted file mode 100644
index bd179e6..0000000
--- a/065-reading-input/reading-input.go
+++ /dev/null
@@ -1,13 +0,0 @@
-// ## Reading Input
-
-package main
-
-import "fmt"
-
-func main() {
-    fmt.Print("Enter a number: ")
-    var input float64
-    fmt.Scanf("%f", &input)    
-    output := input * 2
-    fmt.Println(input, "* 2 =", output)    
-}
diff --git a/065-reading-input/reading-input.sh b/065-reading-input/reading-input.sh
deleted file mode 100644
index f95b609..0000000
--- a/065-reading-input/reading-input.sh
+++ /dev/null
@@ -1,3 +0,0 @@
-$ go run reading-input.go 
-Enter a number: 7
-7 * 2 = 14
diff --git a/068-tcp-client/tcp-client.go b/066-tcp-client/tcp-client.go
similarity index 100%
rename from 068-tcp-client/tcp-client.go
rename to 066-tcp-client/tcp-client.go
diff --git a/068-tcp-client/tcp-client.sh b/066-tcp-client/tcp-client.sh
similarity index 100%
rename from 068-tcp-client/tcp-client.sh
rename to 066-tcp-client/tcp-client.sh
diff --git a/069-http-client/http-client.go b/067-http-client/http-client.go
similarity index 100%
rename from 069-http-client/http-client.go
rename to 067-http-client/http-client.go
diff --git a/070-http-client-basic/http-client-basic.go b/068-http-client-basic/http-client-basic.go
similarity index 100%
rename from 070-http-client-basic/http-client-basic.go
rename to 068-http-client-basic/http-client-basic.go
diff --git a/071-https-client/https-client.go b/069-https-client/https-client.go
similarity index 100%
rename from 071-https-client/https-client.go
rename to 069-https-client/https-client.go
diff --git a/072-redis/redis.go b/070-redis/redis.go
similarity index 100%
rename from 072-redis/redis.go
rename to 070-redis/redis.go
diff --git a/072-redis/redis.sh b/070-redis/redis.sh
similarity index 100%
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rename to 070-redis/redis.sh
diff --git a/073-postgres/postgres.go b/071-postgres/postgres.go
similarity index 100%
rename from 073-postgres/postgres.go
rename to 071-postgres/postgres.go
diff --git a/073-postgres/postgres.sh b/071-postgres/postgres.sh
similarity index 100%
rename from 073-postgres/postgres.sh
rename to 071-postgres/postgres.sh
diff --git a/074-sending-email/sending-email.go b/072-sending-email/sending-email.go
similarity index 100%
rename from 074-sending-email/sending-email.go
rename to 072-sending-email/sending-email.go
diff --git a/075-http-server-basic/http-server-basic.go b/073-http-server-basic/http-server-basic.go
similarity index 100%
rename from 075-http-server-basic/http-server-basic.go
rename to 073-http-server-basic/http-server-basic.go
diff --git a/076-http-server-canonical-host/http-server-canonical-host.go b/074-http-server-canonical-host/http-server-canonical-host.go
similarity index 100%
rename from 076-http-server-canonical-host/http-server-canonical-host.go
rename to 074-http-server-canonical-host/http-server-canonical-host.go
diff --git a/076-http-server-canonical-host/http-server-canonical-host.sh b/074-http-server-canonical-host/http-server-canonical-host.sh
similarity index 100%
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rename to 074-http-server-canonical-host/http-server-canonical-host.sh
diff --git a/077-http-server-graceful-shutdown/http-server-graceful-shutdown.go b/075-http-server-graceful-shutdown/http-server-graceful-shutdown.go
similarity index 100%
rename from 077-http-server-graceful-shutdown/http-server-graceful-shutdown.go
rename to 075-http-server-graceful-shutdown/http-server-graceful-shutdown.go
diff --git a/077-http-server-graceful-shutdown/http-server-graceful-shutdown.sh b/075-http-server-graceful-shutdown/http-server-graceful-shutdown.sh
similarity index 100%
rename from 077-http-server-graceful-shutdown/http-server-graceful-shutdown.sh
rename to 075-http-server-graceful-shutdown/http-server-graceful-shutdown.sh
diff --git a/078-http-server-log/http-server-log.go b/076-http-server-log/http-server-log.go
similarity index 100%
rename from 078-http-server-log/http-server-log.go
rename to 076-http-server-log/http-server-log.go
diff --git a/079-http-server-middleware/http-server-middleware.go b/077-http-server-middleware/http-server-middleware.go
similarity index 100%
rename from 079-http-server-middleware/http-server-middleware.go
rename to 077-http-server-middleware/http-server-middleware.go
diff --git a/080-http-server-routing/http-server-routing.go b/078-http-server-routing/http-server-routing.go
similarity index 100%
rename from 080-http-server-routing/http-server-routing.go
rename to 078-http-server-routing/http-server-routing.go
diff --git a/080-http-server-routing/http-server-routing.sh b/078-http-server-routing/http-server-routing.sh
similarity index 100%
rename from 080-http-server-routing/http-server-routing.sh
rename to 078-http-server-routing/http-server-routing.sh
diff --git a/081-http-server-static-dynamic/http-server-static-dynamic.go b/079-http-server-static-dynamic/http-server-static-dynamic.go
similarity index 100%
rename from 081-http-server-static-dynamic/http-server-static-dynamic.go
rename to 079-http-server-static-dynamic/http-server-static-dynamic.go
diff --git a/081-http-server-static-dynamic/http-server-static-dynamic.sh b/079-http-server-static-dynamic/http-server-static-dynamic.sh
similarity index 100%
rename from 081-http-server-static-dynamic/http-server-static-dynamic.sh
rename to 079-http-server-static-dynamic/http-server-static-dynamic.sh
diff --git a/082-http-server-static-select/http-server-static-select.go b/080-http-server-static-select/http-server-static-select.go
similarity index 100%
rename from 082-http-server-static-select/http-server-static-select.go
rename to 080-http-server-static-select/http-server-static-select.go
diff --git a/082-http-server-static-select/http-server-static-select.sh b/080-http-server-static-select/http-server-static-select.sh
similarity index 100%
rename from 082-http-server-static-select/http-server-static-select.sh
rename to 080-http-server-static-select/http-server-static-select.sh
diff --git a/083-http-server-static/http-server-static.go b/081-http-server-static/http-server-static.go
similarity index 100%
rename from 083-http-server-static/http-server-static.go
rename to 081-http-server-static/http-server-static.go
diff --git a/083-http-server-static/http-server-static.sh b/081-http-server-static/http-server-static.sh
similarity index 100%
rename from 083-http-server-static/http-server-static.sh
rename to 081-http-server-static/http-server-static.sh
diff --git a/084-http-server-status-code/http-server-status-code.go b/082-http-server-status-code/http-server-status-code.go
similarity index 100%
rename from 084-http-server-status-code/http-server-status-code.go
rename to 082-http-server-status-code/http-server-status-code.go
diff --git a/084-http-server-status-code/http-server-status-code.sh b/082-http-server-status-code/http-server-status-code.sh
similarity index 100%
rename from 084-http-server-status-code/http-server-status-code.sh
rename to 082-http-server-status-code/http-server-status-code.sh
diff --git a/085-http-server/http-server.go b/083-http-server/http-server.go
similarity index 100%
rename from 085-http-server/http-server.go
rename to 083-http-server/http-server.go
diff --git a/083-tcp-server/tcp-server.go b/083-tcp-server/tcp-server.go
deleted file mode 100644
index 5abda6e..0000000
--- a/083-tcp-server/tcp-server.go
+++ /dev/null
@@ -1,26 +0,0 @@
-// ## TCP Server
-
-package main
-
-import "net"
-
-func main() {
-    listener, _ := net.Listen("tcp", "0.0.0.0:5000")
-    for {
-        conn, _ := listener.Accept()
-        go Serve(conn)
-    }
-}
-
-func Serve(conn net.Conn) {
-    buf := make([]byte, 1024)
-    for {
-        _, err := conn.Read(buf)
-        if err != nil {
-            conn.Close()
-            return
-        } else {
-            conn.Write(buf)
-        }
-    }
-}
diff --git a/083-tcp-server/tcp-server.sh b/083-tcp-server/tcp-server.sh
deleted file mode 100644
index d7cbd1d..0000000
--- a/083-tcp-server/tcp-server.sh
+++ /dev/null
@@ -1 +0,0 @@
-$ go run tcp-server.go
diff --git a/086-https-server/https-server.go b/084-https-server/https-server.go
similarity index 100%
rename from 086-https-server/https-server.go
rename to 084-https-server/https-server.go
diff --git a/086-https-server/https-server.sh b/084-https-server/https-server.sh
similarity index 100%
rename from 086-https-server/https-server.sh
rename to 084-https-server/https-server.sh
diff --git a/tool/index.txt b/tool/index.txt
index b041c23..289343c 100644
--- a/tool/index.txt
+++ b/tool/index.txt
@@ -69,10 +69,11 @@ urls
 sha1-hashes
 ~ base64-encoding
 
-# systems programming
+# systems libraries
 reading-files
 writing-files
 ~ standard-streams
+line-filter
 command-line-arguments
 command-line-flags
 environment-variables
@@ -80,9 +81,6 @@ spawning-processes
 execing-processes
 signals
 exit
-reading-input
-line-filter
-tcp server
 
 # client libraries
 tcp-client