+
+ /**
+ * Checks whether the given stack is initialized (set in array $stackers)
+ *
+ * @param $stackerName Name of the stack
+ * @return $isInitialized Whether the stack is initialized
+ */
+ function isStackInitialized ($stackerName);
+
+ /**
+ * Checks whether the given stack is empty
+ *
+ * @param $stackerName Name of the stack
+ * @return $isEmpty Whether the stack is empty
+ * @throws NoStackerException If given stack is missing
+ */
+ function isStackEmpty ($stackerName);