diff --git a/notes-and-examples/2026.07.21/main.py b/notes-and-examples/2026.07.21/main.py
new file mode 100644
index 0000000..6c7a782
--- /dev/null
+++ b/notes-and-examples/2026.07.21/main.py
@@ -0,0 +1,25 @@
+# Adjacency list
+first_graph = {
+    1: [3, 20],
+    2: [20],
+    3: [1, 20],
+    20: [2, 3]
+}
+
+# First exercise: go from 1, to 20, to 2
+first_graph[first_graph[1][1]][0]
+
+# pass visited by reference
+def depth_first_search(graph: dict, start, visited=set()):
+    print(start)
+    if len(visited)==len(graph):
+        return visited
+
+    for x in graph[start]:
+        if x not in visited:
+            visited.add(x)
+            return depth_first_search(graph, x, visited)
+    pass
+    
+
+depth_first_search(first_graph, 1)