         return tags.count
     }
     
+    func numberOfBooks() -> Int {
+        return books.count
+    }
+    
     func numberOfBookFromTag(tag: String) -> Int {
         guard let count = dictionary[tag]?.count else {
             return 0

        } else {
            dictionary[favoritesTag] = dictionary[favoritesTag]?.filter({ $0 !== book })
        }
        
        isLibraryChanged = true


    func sort() {
        tags.sortInPlace()
        
        books.sortInPlace(sortClosure)
        
        for tag in self.tags {
            dictionary[tag]?.sortInPlace(sortClosure)
        }
    }
    
