diff --git a/STL/STL-Set/set.cpp b/STL/STL-Set/set.cpp
index ebf0c33..b7e2ef4 100644
--- a/STL/STL-Set/set.cpp
+++ b/STL/STL-Set/set.cpp
@@ -22,6 +22,7 @@ int main(){
 	cout << endl;
 	cout << a.count(3) << endl;
 	a.erase(6);
+	//没有.at()和a[i]，树结构，不能直接访问第i个，可以it++ 
 	for(auto it = a.begin(); it != a.end(); it++){
 		cout << *it << " ";
 	}
diff --git a/STL/STL-map/map.cpp b/STL/STL-map/map.cpp
index 222a8fb..9d98733 100644
--- a/STL/STL-map/map.cpp
+++ b/STL/STL-map/map.cpp
@@ -16,6 +16,7 @@ int main(int argc, char* argv[]){
 	 b.insert(make_pair(3,"333"));
 	 b.emplace(make_pair(4,"444"));
 	 cout << b.count(3) << endl;
+	//没有.at()和a[i]，树结构，不能直接访问第i个，可以it++ 
 	 for(auto it = b.begin(); it != b.end(); it++){
 	 	cout << it->first << ", " << it->second << " ";
 	 }
diff --git a/STL/STL-map/multimap.cpp b/STL/STL-map/multimap.cpp
new file mode 100644
index 0000000..4ed5852
--- /dev/null
+++ b/STL/STL-map/multimap.cpp
@@ -0,0 +1,31 @@
+#include <iostream>
+#include <map>
+using namespace std;
+
+bool cmp(int a, int b){
+	return a < b;
+}
+
+int main(){
+	auto cmpl = [](int a, int b){
+		return a > b;
+	};
+	multimap<int, string, bool(*)(int, int)> a(cmp);
+	multimap<int, string, decltype(cmpl)> b(cmpl);
+	a.insert({{1,"111"},{2,"222"},{1,"11"},{1,"1"},{2,"22"},{3,"333"}});//emplace只能用make_pair，不能直接这么写
+	//pair<const int, string>，Key是const修饰的 
+	for(pair<int, string> x : a){
+		cout << x.first << ", " << x.second << " "; 
+	}
+	cout << endl;
+	cout << a.find(1)->second << " " << a.count(1) << endl; 
+	a.erase(a.find(1));
+	cout << a.find(1)->second << " " << a.count(1) << endl;
+	return 0;
+} 
+/*
+1, 111 1, 11 1, 1 2, 222 2, 22 3, 333
+111 3
+11 2
+*/
+
diff --git a/STL/STL-map/multimap.exe b/STL/STL-map/multimap.exe
new file mode 100644
index 0000000..12a5e44
Binary files /dev/null and b/STL/STL-map/multimap.exe differ
diff --git a/STL/STL-unordered_map/README.MD b/STL/STL-unordered_map/README.MD
new file mode 100644
index 0000000..e69de29
diff --git a/STL/STL-unordered_set/README.MD b/STL/STL-unordered_set/README.MD
new file mode 100644
index 0000000..e69de29