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 = list(input() for _ in range(h))
    if sum(a.count('#') for a in s) & 1:
        return "NO"
    m = set()
    for i in range(h):
        for j in range(w):
            if s[i][j] == '#':
                m.add((i, j))
    len_m = (len(m) - 2) // 2
    a = min(m)
    m.remove(a)
    for b in m:
        y = b[0] - a[0]
        x = b[1] - a[1]
        if f(m - {b}, y, x, len_m):
            return "YES"
    return "NO"
print(solve())