#include <iostream>
#include <vector>

using namespace std;

int main()
{
    int R, C, A, B;
    cin >> R >> C >> A >> B;

    vector<int> a_i;
    vector<int> b_i;
    int X = A;
    while(X--){
        int in;
        cin >> in;
        a_i.push_back(in);
    }
    X = B;
    while(X--){
        int in;
        cin >> in;
        b_i.push_back(in);
    }
    int EvenOrOdd = 0;
    int EvenOrOdd2 = 0;
    for (int i = 0; i < R; i++)
    {
        if (a_i.front() == 0)
        {
            a_i.erase(a_i.begin());
            EvenOrOdd2++;
        }
        vector<int> save = b_i;
        while (!save.empty())
        {
            if (save.front() == 0)
            {
                save.erase(save.begin());
                EvenOrOdd++;
            }
            else if (save.front() > 0)
            {
                if (EvenOrOdd2 % 2 == 0)
                {
                    if (EvenOrOdd % 2 == 0)
                        cout << "B";
                    else
                        cout << "W";
                }
                else
                {
                    if (EvenOrOdd % 2 == 0)
                        cout << "W";
                    else
                        cout << "B";
                }

                save.front()--;
            }
        }
        cout << endl;
        a_i.front()--;
    }
    return 0;
}