(also known as " ", " ") is a type of logic puzzle published by Nikoli. The goal is to draw a single continuous non-intersecting loop that connects the centers of the grid cells. The loop may not pass through any cells which contain arrows. The loop may only travel horizontally or vertically, and never diagonally. Any cell that does not have an arrow and which is not part of the loop must be shaded in black. Black cells do not touch each other orthogonally (they do not share a side). A cell containing a number and an arrow represents how many black cells are in the row or column pointed at by the arrow. There may be black cells that are not accounted for by the cells with arrows and numbers.