#include<bits/stdc++.h>
#include<ext/pb_ds/assoc_container.hpp>
#include<ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
using namespace std;
tree<pair<int,int>,null_type,less<pair<int,int>>,rb_tree_tag,tree_order_statistics_node_update>ss,tt;
int main(){
	ss.insert({0,0});
	ss.insert({2,1});
	tt.insert({1,2});
	ss.join(tt);
	
	return 0;

}

求助，为什么join_error?