h,w = map(int,input().split())
s = [list(input()) for i in range(h)]
c = 0
for x in s: c += x.count("#")
if c == 0:
    print("NO")
    exit()

for i in range(h+1):
    for j in range(-w, w+1):
        use = [[0 for _ in range(w)] for __ in range(h)]
        if i == j == 0: continue
        flg = True
        for x in range(h):
             for y in range(w):
                 if s[x][y] == "#" and use[x][y] == 0:
                    if 0 <= x+i < h and 0 <= y+j < w and s[x+i][y+j] == "#" and use[x+i][y+j] == 0:
                        use[x][y] = 1
                        use[x+i][y+j] = 1
                    else:
                        flg = False
        cc = 0
        for x in use: cc += x.count(1)
        if flg and c == cc:
            print("YES")
            exit()
print("NO")