#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
char a[1000007];
char b[1000007];
int aa[100],bb[100];
int main()
{
	ll t;
	cin>>t;
	while(t--){
		int n,k;
		cin>>n>>k;
		scanf("%s",a+1);
		scanf("%s",b+1);
		for(int i=1;i<=30;i++)aa[i]=bb[i]=0;
		for(int i=1;i<=n;i++){
			aa[a[i]-'a'+1]++;
			bb[b[i]-'a'+1]++;
		}
		for(int i=1;i<=26;i++){
			while(aa[i]!=0&&bb[i]!=0){
				aa[i]--;
				bb[i]--;
			}
		}
		int flag=0;
		for(int i=1;i<=26;i++){
			if(bb[i]!=0)
			for(int j=1;j<=i;j++){
				if(bb[i]%k!=0||aa[i]%k!=0)flag=1;
				if(aa[j]!=0&&j!=26){
					if(aa[j]<bb[i]){
						bb[i]-=aa[j];
						aa[j]=0;
					}	
					else{
						aa[j]-=bb[i];
						bb[i]=0;
						break;
					}
				}
			}
			if(bb[i]!=0){
				flag=1;
				break;
			}	
		}
		if(flag==1)printf("No\n");
		else printf("Yes\n");	
		}
	return 0;
}