#include <iostream>
#include <vector>
#include <string>

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

  std::vector<int> row_heights;

  for (int i = 0; i < A; i++) {
    int row_height;
    std::cin >> row_height;

    row_heights.push_back(row_height);
  }

  std::vector<int> col_widths;

  for (int i = 0; i < B; i++) {
    int col_width;
    std::cin >> col_width;

    col_widths.push_back(col_width);
  }

  bool white = false;

  for (int row_height : row_heights) {
    for (int zed = 0; zed < row_height; zed++) {
      for (int col_width : col_widths) {
        for (int a = 0; a < col_width; a++) {
          std::cout << (white ? 'W' : 'B');
        }
        if (col_width != 1) {
          white = !white;
        }
      }
      std::cout << "\n";
    }
    white = !white;
  }
}