#include <bits/stdc++.h>
#define sz(x) (int)(x).size()
#define all(x) (x).begin(), (x).end()
#define st first
#define nd second
using namespace std;
typedef long long ll;
const int mod = 1e9 + 7;
const int N = 1e6 + 5;
vector<pair<int, int>> adj[N];
int cnt[N], ans[N], n, m, k;

void dfs(int u, int p = -1) {
	if (u < k)
		ans[u] = p < n;
	for (; cnt[u] < size(adj[u]);) {
		auto [v, i] = adj[u][cnt[u]];
		cnt[u]++;
		if (i == -1) 
			continue;
		adj[v][i].second = -1;
		dfs(v, u);
	}
}

void solve() {
	k = N; cin >> n >> m;
	for (int i = 0; i < n + m; i++)
		adj[i].clear(), cnt[i] = ans[i] = 0;
	vector<int> deg(n + m);
	for (int i = 0; i + 1 < n; i++) {
		int p; cin >> p; p--;
		k = min(k, p);
		if (i >= k && deg[i] % 2 == 0)
			continue;
		deg[p]++;
		adj[i].emplace_back(p, size(adj[p]));
		adj[p].emplace_back(i, size(adj[i]) - 1);
	}
	for (int i = 0; i + 1 < m; i++) {
		int p; cin >> p; p--;
		int j = i < k ? i : i + n;
		if (j >= k && deg[j] % 2 == 0)
			continue;
		deg[p + n]++;
		adj[j].emplace_back(p + n, size(adj[p + n]));
		adj[p + n].emplace_back(j, size(adj[j]) - 1);
	}
	if (adj[n + m - 1].empty())
		dfs(k);
	else
		dfs(n + m - 1);
	string s(k, 'R');
	for (int i = 0; i < k; i++)
		if (ans[i])
			s[i] = 'B';
	cout << s << endl;
}

int main() {
	ios_base::sync_with_stdio(false); cin.tie(0);
	int t; cin >> t; while (t--) solve();
}