diff --git a/.obsidian/workspace.json b/.obsidian/workspace.json
index d76ef88..8383a6a 100644
--- a/.obsidian/workspace.json
+++ b/.obsidian/workspace.json
@@ -201,10 +201,10 @@
   },
   "active": "fcc28e70ad8acbd2",
   "lastOpenFiles": [
-    "Discrete Structures/Mathematical Data Structures.md",
     "Discrete Structures/Mathematical Proofs (Induction).md",
     "Discrete Structures/Recurrence relations.md",
     "Discrete Structures/Relations and Digraphs.md",
+    "Discrete Structures/Mathematical Data Structures.md",
     "Discrete Structures/Counting.md",
     "Languages & Machines/Regular languages.md",
     "Software Engineering/Meeting.md",
diff --git a/Languages & Machines/Regular languages.md b/Languages & Machines/Regular languages.md
index 04e82eb..36822ea 100644
--- a/Languages & Machines/Regular languages.md	
+++ b/Languages & Machines/Regular languages.md	
@@ -45,4 +45,17 @@ $|w| = n \geq 1$, so $w = u a$ with $|u| = n-1$,
 ## Operations on languages
 - Lifting operations on strings to languages
 - Concatenation of languages
-- Kleene star - 
\ No newline at end of file
+- Kleene star - $V^*$ -> smallest superset[^1] of V that contains the empty string and is closed under concatenation, i.e. one or more repetitions
+- Reversal
+
+## Regular sets / languages
+This used to be in DS, but I don't have it in this repo.
+
+Recursively defined over an alphabet $\Sigma$ from 
+- $\emptyset$
+- $\{\epsilon\}$
+- $\{a\} | \forall a \in \Sigma$
+
+Regex is  a notatio nto denote regular languages, i.e.:
+
+[^1]: The opposite of a subset - a set which contains all elements of another (and possibly more)