diff --git a/.gitignore b/.gitignore
index f64677d..98629db 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,3 @@
 i
 s
-
+t
diff --git a/track.cpp b/track.cpp
new file mode 100644
index 0000000..3af2fa3
--- /dev/null
+++ b/track.cpp
@@ -0,0 +1,30 @@
+#include <iostream>
+#include <ostream>
+class A {
+  long long counter = 0;
+
+public:
+  A() : counter{0} {}
+  A operator()() {
+    A ret = *this;
+    ret.counter++;
+    return ret;
+  }
+  A operator[](int dummy) {
+    A ret = *this;
+    ret.counter--;
+    return ret;
+  }
+  friend std::ostream &operator<<(std::ostream &lhs, A const &rhs) {
+    lhs << rhs.counter;
+    return lhs;
+  }
+};
+
+int main(void) {
+  A a;
+  std::cout << a[0] << std::endl;
+  std::cout << a[0]() << std::endl;
+  std::cout << a[0]()() << std::endl;
+  return 0;
+}