/** gnu specific **/
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
/** contains everything I need in std **/
#include <bits/stdc++.h>

#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define sz(S) ((int)S.size())
#define FOR(i, st_, n) for(int i = st_; i < n; ++i)
#define RFOR(i, n, end_) for(int i = (n)-1; i >= end_; --i)
#define x first
#define y second
#define pb push_back
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<ll, ll> pll;
typedef pair<int, int> pii;
typedef pair<double, double> pdd;
typedef unsigned long long ull;
typedef long double LD;
typedef pair<ull, ull> pull;
using namespace __gnu_pbds;
typedef tree<ll, null_type, less<>, rb_tree_tag, tree_order_statistics_node_update> ordered_set;
using namespace std;
#ifdef ONPC
mt19937 rnd(228);
#else
mt19937 rnd(chrono::high_resolution_clock::now().time_since_epoch().count());
#endif

/*

1 2 3
3 2

BBBWW
WWWBB
WWWBB
BBBWW
BBBWW
BBBWW
*/

int solve()
{
	int n, m, A, B;
	if(!(cin>>n>>m>>A>>B))return 1;
	vector<int> a(A);
	vector<int> b(B);
	FOR(i,0,A)cin>>a[i];
	FOR(i,0,B)cin>>b[i];
	vector<vector<bool>> M(n, vector<bool>(m, false));

	int k=0;
	int J=0;
	FOR(i,0,m)
	{
		int j = 0;
		if(k == b[J]) ++J, k=0;
		++k;
		bool ok = (J%2==0);

		for(auto c: a)
		{
			for(int ctr=0; ctr<c; ++ctr, ++j)
				M[j][i]=ok;
			ok=!ok;
		}
	}
	
	FOR(i,0,n)
	{
		FOR(j,0,m)
		{
			if(M[i][j])cout<<"B";
			else cout<<"W";
		}
		cout<<'\n';
	}
    return 0;
}

int32_t main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    int TET = 1e9;
    //cin >> TET;
    for (int i = 1; i <= TET; i++)
    {
        if (solve())
        {
            break;
        }
#ifdef ONPC
        cout << "__________________________" << endl;
#endif
    }
#ifdef ONPC
    cerr << endl << "finished in " << clock() * 1.0 / CLOCKS_PER_SEC << " sec" << endl;
#endif
}