import copy
H,W=int(input())
S=[]
for i in range(H):
    S.append(input())

cnt_black = sum(S[i].count('#') for i in range(H))
if cnt_black %2 == 1:
    print('NO')
    exit()

for h in range(H):
    for w in range(W):
        if h==0 and w==0:
            continue
        s = copy.deepcopy(S)
        for i in range(H):
            for j in range(W):
                cnt = 0
                if s[i][j] == '#':
                    if 0 <= i+h < H and 0 <= j+w <W and s[i+h][j+w] == '#':
                        s[i][j] = 'r'
                        s[i+h][j+w] = 'b'
                        cnt += 2
                    else:
                        break
            if cnt == cnt_black:
                print('YES')
                exit()
print('NO')