h, w = map(int, input().split())
S = []
for i in range(h):
    S.append(input())

cnt = 0
D = set()
for ss in S:
    for s in ss:
        cnt += 1
        if s == "#":
            D.add(cnt)

l = len(D)
if l & 1:
    print("NO")
    exit()

flg = False
m = max(D)
for i in range(1, m):
    cnt = 0
    tmp = []
    for d in D:
        if d in tmp:
            continue
        elif d + i in D:
            cnt += 1
            tmp.append(d + i)
    #print(i, cnt, tmp)
    if l // 2 == cnt:
        #print(i,cnt,tmp)
        flg = True
print("YES" if flg else "NO")