unique var names in example

CppCoreGuidelines.md

@@ -13044,8 +13044,8 @@ Better performance, better compile-time checking, guaranteed compile-time evalua
 ##### Example
 
     double x = f(2);            // possible run-time evaluation
-    const double x = f(2);      // possible run-time evaluation
-    constexpr double y = f(2);  // error unless f(2) can be evaluated at compile time
+    const double y = f(2);      // possible run-time evaluation
+    constexpr double z = f(2);  // error unless f(2) can be evaluated at compile time
 
 ##### Note