#include<iostream>
#include<bits/stdc++.h>
using namespace std;
typedef long long int ll;
ll max(ll a,ll b){
    if(a>b)return a;
    return b;
}
int main(){
    int T;
    cin>>T;
    while(T--){
        int n,k;
        cin>>n>>k;
        string s1,s2;
        cin>>s1;
        cin>>s2;
        vector<int>c1(26,0),c2(26,0);
        for(int i=0;i<s1.length();i++){
            c1[s1[i]-'a']++;
        }
        for(int i=0;i<s2.length();i++){
            c2[s2[i]-'a']++;
        }
        for(int i=0;i<26;i++){
            if(c1[i]==c2[i]){
               c1[i]=0;
               c2[i]=0;
            }
            else if(c1[i]<c2[i]){
                c2[i]-=c1[i];
                c1[i]=0;
            }
            else{
                c1[i]-=c2[i];
                c2[i]=0;
            }
        }
        int f=0;
        int j=25;int i=25;
        while(j>=0 && i>=0){
            if(c1[i]==0){
               i--;
               continue;
            }
            if(c2[j]==0){
               j--;
               continue;
            }
            if(i>j){
               f=1;
               break;
            }
       
            if(c1[i]%k!=0){
               f=1;
               break;
           }
            if(c2[j]%k!=0){
               f=1;
               break;
            }
            if(c1[i]==c2[j]){
               c1[i]=0;
               c2[j]=0;
               i--;
               j--;
               
            }
            else if(c1[i]>c2[j]){
               c1[i]-=c2[j];
               j--;
            }
            else{
               c2[j]-=c1[i];
               i--;
            }
        }
        if(f==1)
        cout<<"NO"<<endl;
        else
        cout<<"YES"<<endl;
    }
}
