import sys
from collections import defaultdict, Counter
from itertools import permutations
from functools import cache
input = sys.stdin.readline

############ ---- Input Functions ---- ############
def inp(): # For taking integer inputs.
    return(int(input()))

def inlst(): # For taking List inputs.
    return(list(map(int,input().split())))

# For taking string inputs. Actually it returns a List of Characters, instead of a string, 
def instr():
    s = input()
    return(list(s[:len(s) - 1]))

# For taking space seperated integer variable inputs.
def insep(): 
    return(map(int,input().split()))

############ ---- Problem ---- ############

R, C, A, B = inlst()
a = [inp() for _ in range(A)]
b = [inp() for _ in range(B)]

grid = []

cur_row = 0
col_count = 0
row_count = 0

for row in range(R):
    l = []
    for i, rec in enumerate(b):
        # print(cur_row)
        c = "W" if cur_row % 2 else "B"
        if i % 2 != 0:
            c = "B" if cur_row % 2 else "W"
        l.extend([c]*rec)
    grid.append(l)
    row_count += 1
    # print(row_count, a[c_row])
    if row_count == a[cur_row]:
        cur_row += 1
        row_count = 0
        # print("New row")
        

for row in grid:
    print("".join(row))