class LIST:
    __slots__ = ['li', 'len_li', 'err', 'b', 'ma', 'left', 'right']
    def __init__(self, li, err):
        self.li = li
        self.len_li = len(li)
        self.err = err
        self.b = [0] * self.len_li
        self.ma = {a:i for i, a in enumerate(li)}
        self.left = 0
        self.right = self.len_li - 1
    def __len__(self):
        return self.b.count(0)
    def reset(self):
        self.b = [0] * self.len_li
        self.left = 0
    def pop(self):
        for i in range(self.right, self.left - 1, -1):
            if self.b[i] == 0:
                self.b[i] = 1
                for j in range(i - 1, self.left - 1, -1):
                    if self.b[j] == 0:
                        self.right = j
                        break
                return self.li[i]
        return self.err
    def pop(self, a):
        self.b[a] = 1
        return self.li[a]
    def popleft(self):
        for i in range(self.left, self.len_li):
            if self.b[i] == 0:
                self.b[i] = 1
                for j in range(i + 1, self.len_li):
                    if self.b[j] == 0:
                        self.left = j
                        break
                return self.li[i]
        return self.err
    def find(self, a):
        if a in self.ma and self.b[self.ma[a]] == 0:
            return True
        return False
    def remove(self, a):
        if self.find(a):
            self.b[self.ma[a]] = 1
            return True
        return False
def f(m, yx, n):
    for _ in range(n):
        if not m.remove(m.popleft() + yx):
            return False
    return True
def solve():
    h, w = map(int, input().split())
    s = tuple(input() for _ in range(h))
    m = tuple(complex(i, j) for i in range(h) for j in range(w) if s[i][j] == '#')
    if m == () or len(m) & 1:
        return "NO"
    a = m[0]
    dp = LIST(m[1:], complex(-100, -100))
    n = len(dp) // 2
    for i in range(len(dp)):
        if f(dp, dp.pop(i) - a, n):
            return "YES"
        dp.reset()
    return "NO"
print(solve())