renamed variables for an easier understanding

src/de/schleifen/Schleifen.java

@@ -17,11 +17,11 @@ public class Schleifen {
     }
 
     public static void halberTannenbaum() {
-        String x = "x";
+        String a = "x";
         for (int i=0; i<13; i++) {
-            String y = x + "x";
+            String b = a + "x";
-            System.out.println(x);
+            System.out.println(a);
-            x = y;
+            a = b;
         }
     }
 }