Akari Masyu Instructions

Rules: The challenge is to draw a loop around the grid and light up all white cells, subject to the following rules:

1. White circles must be travelled straight through, but the loop must turn in the previous and/or next intersection in its path.
2. Black circles must be turned upon, but the loop must travel straight through the next and previous intersections in its path.
3. The loop mustn't cross or branch off.
4. Numbers in the squares represent how many of its four sides contain a lit cell.
5. All White cells must contain part of the loop or a lit cell.
6. Each lit cell illuminates all white cells in a horizontal and vertical direction until the beam hits a black cell or a wall.
7. Lights cannot shine on each other.