def f(m, y, x, len_m):
    for _ in range(len_m):
        a = min(m)
        ny = y + a[0]
        nx = x + a[1]
        if (ny, nx) not in m:
            return False
        m.remove(a)
        m.remove((ny, nx))
    return True
def solve():
    h, w = map(int, input().split())
    s = tuple(input() for _ in range(h))
    c_cnt = sum(a.count('#') for a in s)
    if c_cnt == 0 or c_cnt & 1:
        return "NO"
    m = {(i, j) for i in range(h) for j in range(w) if s[i][j] == '#'}
    a = min(m)
    m.remove(a)
    c_cnt = (c_cnt - 2) // 2
    for b in m:
        y = b[0] - a[0]
        x = b[1] - a[1]
        if f(m - {b}, y, x, c_cnt):
            return "YES"
    return "NO"
print(solve())