#include <iostream>
#include <string>
#include <sstream>
#include <vector>
#include <fstream>



class inputParams {
private:
  std::vector<std::string> split (const std::string &s, char delim) {
    std::vector<std::string> result;
    std::stringstream ss (s);
    std::string item;

    while (getline (ss, item, delim)) {
        result.push_back (item);
    }

    return result;
  }

public:
  int rows;
  int cols;
  int wideRows;
  int wideCols;
  std::vector<int> rowSizes;
  std::vector<int> colSizes;

  inputParams(std::istream& input) {
    read(input);
  }

  void read(std::istream& input) {
    std::string line;

    std::getline(input, line);
    std::vector<std::string> lsplit = split(line, ' ');

    rows = std::stoi(lsplit.at(0));
    cols = std::stoi(lsplit.at(1));
    wideRows = std::stoi(lsplit.at(2));
    wideCols = std::stoi(lsplit.at(3));

    for(int i = 0; i < wideRows; ++i) {
      std::getline(input, line);
      rowSizes.push_back(std::stoi(line));
    }

    for(int i = 0; i < wideCols; ++i) {
      std::getline(input, line);
      colSizes.push_back(std::stoi(line));
    }
  }
};

std::string printChecker(const std::vector<int>& rows, const std::vector<int>& cols) {
  bool rowStartColor = true;
  bool checkerColor = true;
  std::string output;

  for(int ri = 0; ri < rows.size(); ++ri) {
    for(int rj = 0; rj < rows.at(ri); ++rj) {
      std::string line;
      checkerColor = rowStartColor;

      for(int ci = 0; ci < cols.size(); ++ci) {
        for(int cj = 0; cj < cols.at(ci); ++cj) {
          if(checkerColor) {
            line += "B";
          } else {
            line += "W";
          }
        }

        checkerColor = !checkerColor;
      }

      output += line + "\n";
    }

    rowStartColor = !rowStartColor;
  }

  return output;
}


int main() {
  inputParams input(std::cin);

  std::string output;
  output = printChecker(input.rowSizes, input.colSizes);

  std::cout << output;

  return 0;
}