diff --git a/src/fsm.rs b/src/ch04_machinery/fsm.rs
similarity index 98%
rename from src/fsm.rs
rename to src/ch04_machinery/fsm.rs
index bd15636..dac3b1a 100644
--- a/src/fsm.rs
+++ b/src/ch04_machinery/fsm.rs
@@ -1,3 +1,5 @@
+#![allow(unused)]
+
 #[derive(Debug, PartialEq, Copy, Clone)]
 enum State {
     Idle,
diff --git a/src/ch04_machinery/mod.rs b/src/ch04_machinery/mod.rs
new file mode 100644
index 0000000..9115837
--- /dev/null
+++ b/src/ch04_machinery/mod.rs
@@ -0,0 +1,2 @@
+mod fsm;
+mod turing;
diff --git a/src/turing.rs b/src/ch04_machinery/turing.rs
similarity index 99%
rename from src/turing.rs
rename to src/ch04_machinery/turing.rs
index d60f10b..cbdb020 100644
--- a/src/turing.rs
+++ b/src/ch04_machinery/turing.rs
@@ -1,3 +1,4 @@
+#![allow(unused)]
 type State = usize;
 
 #[derive(Debug, PartialEq, Clone)]
diff --git a/src/lib.rs b/src/lib.rs
index 30c96e0..7518afd 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,2 +1 @@
-pub mod fsm;
-pub mod turing;
+mod ch04_machinery;