#include<bits/stdc++.h>
using namespace std;
#define rep(i,a,b) for(int i=(int)a;i<(int)b;i++)
#define all(p) p.begin(),p.end()
using ll =long long;

struct uf{
    int n;
    vector<int> par;
    uf(int n_):n(n_){
        par.resize(n);
        rep(i,0,n) par[i]=i;
    }
    int root(int a){
        if(a==par[a]) return a;
        par[a]=root(par[a]);
        return par[a];
    }
    int unite(int a,int b){
        a=root(a),b=root(b);
        if(a==b) return 0;
        if(a>b) swap(a,b);
        par[b]=a;
        return 1;
    }
};

void solve(){
    int N,M;
    cin>>N>>M;
    vector<int> p(N-1),q(M-1);
    int K=N;
    rep(i,0,N-1) cin>>p[i],p[i]--,K=min(p[i],K);
    rep(i,0,M-1) cin>>q[i],q[i]--,K=min(q[i],K);
    uf T(K*2);
    auto f=[&](ll n,vector<int> v) -> void {
        vector<int> tmp(n,-1);
        rep(i,0,K){
            tmp[i]=i;
        }
        rep(i,0,n-1){
            if(tmp[i]==-1) continue;
            if(tmp[v[i]]==-1) tmp[v[i]]=tmp[i];
            else{
                int a=tmp[i],b=tmp[v[i]];
                tmp[v[i]]=-1;
                T.unite(2*a,2*b+1);
                T.unite(2*a+1,2*b);
            }
        }
    };
    f(N,p),f(M,q);
    rep(i,0,K) cout<<(T.root(i)&1?'R':'B');
    cout<<"\n";
}

int main(){
    int T;
    cin>>T;
    while(T--) solve();
}

/*
2
7 7
5 5 6 6 7 7
5 6 5 6 7 7
5 4
4 4 5 5
4 4 4
 */