diff --git a/fsm.md b/fsm.md
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--- /dev/null
+++ b/fsm.md
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+# FSM
+
+- Finite state machines. A computation abstraction level that I find particularly appealing for some reason.
+
diff --git a/journal/2020-11-25.md b/journal/2020-11-25.md
index 39f1c052c..460012f41 100644
--- a/journal/2020-11-25.md
+++ b/journal/2020-11-25.md
@@ -5,6 +5,7 @@
 - Remembered I have next Monday off ([[2020-11-30]]) and felt happy.
 - Set up [[autofs]] so SD cards get automounted in Debian. Usually this is done by the desktop environment but in [[i3]] it needs manual setup (I don't mind).
 - Read on [[equanimity]].
+- Read on [[push down automata]]s.
 
 [//begin]: # "Autogenerated link references for markdown compatibility"
 [agora-protocol]: ../agora-protocol "Agora Protocol"
diff --git a/push-down-automata.md b/push-down-automata.md
new file mode 100644
index 000000000..cd1a9a54a
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+++ b/push-down-automata.md
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+# Push down Automata
+
+- Back in school I learnt about [[FSM]]s but not about PDAs for some reason.
+- As I expected (remembered?) they are like FSMs plus a stack.
+