def func(d, r, field):
    find = False
    for y in range(len(field)):
        for x in range(len(field[y])):
            if field[y][x] == '#':
                ny = y + d
                nx = x + r
                if 0 <= ny < len(field) and 0 <= nx < len(field[y]) and field[ny][nx] == '#':
                    find = True
                    field[y][x] = 0
                    field[ny][nx] = 1
                else:
                    return False

    for line in field:
        if '#' in line:
            return False

    return find


def main():
    h, w = map(int, input().split())
    field = []
    for _ in range(h):
        field.append(list(input()))

    for i in range(-50, 50):
        for j in range(-50, 50):
            if i == 0 and j == 0:
                continue

            if func(i, j, [[i for i in j] for j in field]):
                print("YES")
                return
    print("NO")
    
if __name__ == '__main__':
    main()