diff --git a/qualdev/debog/exo4.ts b/qualdev/debog/exo4.ts
new file mode 100644
index 0000000000000000000000000000000000000000..3807df9aa905a88d8852380a64d50d7ac24082b3
--- /dev/null
+++ b/qualdev/debog/exo4.ts
@@ -0,0 +1,10 @@
+function deb3(xy: number[]): void {
+    let tmp = xy[0];
+    xy[0] = xy[1];
+    xy[1] = tmp;
+    console.log(xy);
+}
+
+let xy = [10, 20];
+deb3(xy);
+console.log(xy);
\ No newline at end of file