import sys

H, W = map(int, input().split())

black_l = []
count = 0

for i in range(H):
    l = list(input())
    for j in range(W):
        if l[j] == "#":
            black_l.append(H * i + j)
            count += 1

if count == 0:
    print("NO")
    sys.exit()

if count % 2 == 0:
    num = count // 2
else:
    print("NO")
    sys.exit()

for i in range(H):
    for j in range(W):
        if i == j == 0:
            continue
        nowuse = list(black_l)
        nowuse1 = list(black_l)
        while True:
            if (nowuse[0] % H) + j > W - 1:
                break
            ck_nom = nowuse[0] + j + i * H
            try:
                nowuse.remove(ck_nom)
                nowuse.pop(0)
            except:
                # print(i,j)
                # print(nowuse)
                break
            if len(nowuse) == 0:
                print("YES")
                sys.exit()
        while True:
            if (nowuse1[0] % H) - j < 0:
                break
            ck_nom = nowuse1[0] - j + i * H
            try:
                nowuse1.remove(ck_nom)
                nowuse1.pop(0)
            except:
                # print(i,j)
                # print(nowuse)
                break
            if len(nowuse1) == 0:
                print("YES")
                sys.exit()        

print("NO")