#include<bits/stdc++.h>
using namespace std;
#define int long long
bool tm(string s)
{
     int n = s.size();
     for(int i=1;i<n;i++)
     {
         if(s[i]<s[i-1]) return false;
     }
     return true;
}
int32_t main()
{
	int t; cin>>t;
	while(t--)
    {
        int n; cin>>n ;
        string s1,s2; cin>>s1>>s2;
        char c = min(s1[0],s2[0]);
        string s ="";
        s+=c;
        for(int i=1;i<n;i++)
        {

            if(s2[i]<s1[i] )
            {
                if(s[i-1]<=s2[i]) s+=s2[i];
                else s+=s1[i];

            }
            else
            {
                if(s[i-1]<=s1[i]) s+=s1[i];
                else s+=s2[i];
            }
        }
       
        if(is_sorted(s.begin(),s.end()) )
        {
            cout<<"Yes\n";
        }
        else  cout<<"No\n";
    }

	return 0;
}