#include <bits/stdc++.h>
using namespace std;

#define sz(x) (int)(x).size()
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define pb push_back
#define x first
#define y second
#define FOR(i, a, b) for(int i = (a); i < (b); i++)
#define RFOR(i, a, b) for(int i = (a) - 1; i >= (b); i--)

typedef long long ll;
typedef double db;
typedef long double LD;
typedef pair<int, int> pii;
typedef pair<db, db> pdd;
typedef pair<ll, ll> pll;


int solve()
{
	int r, c, a, b;
	if (!(cin >> r >> c >> a >> b))
		return 1;
	
	vector<int> as(a), bs(b);
	FOR (i, 0, a)
		cin >> as[i];
	FOR (i, 0, b)
		cin >> bs[i];
		
	vector<string> ans(r, string(c, '~'));
	
	auto getStart = [&]() -> pii
	{
		FOR (i, 0, r)
		{
			FOR (j, 0, c)
			{
				if (ans[i][j] == '~')
					return pii{i, j};
			}
		}
		assert(false);
	};
	
	//int bl = 1;
	string str = "BW";
	FOR (i, 0, a)
	{
		FOR (j, 0, b)
		{
			int rr = as[i];
			int cc = bs[j];
			pii st = getStart();
			FOR (ii, st.x, st.x + rr)
			{
				FOR (jj, st.y, st.y + cc)
				{
					ans[ii][jj] = str[(i + j) & 1];
				}
			}
			//bl ^= 1;
		}
		//if (c != 1)
			//bl ^= 1;
	}
	
	for (string sss: ans)
		cout << sss << '\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
			cerr << "_____________________________\n";
		#endif
	}
	#ifdef ONPC
		cerr << "\nfinished in " << clock() * 1.0 / CLOCKS_PER_SEC << " sec\n";
	#endif
	return 0;
}