diff --git a/src/1-ds/pbds.cpp b/src/1-ds/pbds.cpp
index 3ed73ae..87af3a4 100644
--- a/src/1-ds/pbds.cpp
+++ b/src/1-ds/pbds.cpp
@@ -2,7 +2,15 @@
 #include <ext/pb_ds/assoc_container.hpp>
 #include <ext/pb_ds/tree_policy.hpp>
 using namespace __gnu_pbds;
-using ordered_set = tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update>;
-ordered_set st;
+using pbds = tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update>;
+pbds st;
 st.order_of_key(x);  // number of elements strictly less than x
-st.find_by_order(x); // value of xth element (0-based)
\ No newline at end of file
+st.find_by_order(x); // value of xth element (0-based)
+
+// multiset pbds (use "less_equal<int>" and custom "m_erase")
+using multi_pbds = tree<int, null_type, less_equal<int>, rb_tree_tag, tree_order_statistics_node_update>;
+void m_erase(multi_pbds &OS, int val) {
+  int index = OS.order_of_key(val);
+  multi_pbds::iterator it = OS.find_by_order(index);
+  OS.erase(it);
+}