H, W = map(int, input().split())

grid = []
for y in range(H):
    grid.append(input())

def check(dx, dy):
    if dx == 0 and dy == 0:
        return False
    used = {}
    for y in range(H):
        for x in range(W):
            if grid[y][x] != '#':
                continue
            if (x, y) in used:
                continue
            used[(x, y)] = True
            ny = y + dy
            nx = x + dx
            if ny >= H or nx >= W:
                return False
            if grid[ny][nx] != '#':
                return False
            used[(nx, ny)] = True
    return True

ans = False

for dy in range(H):
    for dx in range(W):
        ans = ans or check(dx, dy)


print("YES" if ans else "NO")