Moon-or-Sun (taken from Nikoli)

• Draw a line to make a single loop.
• Lines pass through the centers of cells, horizontally, vertically, or turning. The loop never crosses itself, branches off, or goes through the same cell twice.
• A rectangle, bordered by bold lines, is called a "room". The loop goes through each room exactly one time. Once the loop leaves a room, it cannot return to enter this room.
• In each room, the loop goes through all of the moon cells or all of the sun cells. The loop cannot pass through both moon cells and sun cells in one room.
• After the loop goes through the moons in one room it has to go through all the suns in the next room it enters and visa versa.

Moon-or-Sun (adapted from Nikoli)

• Draw a line to make a single loop.
• Lines pass through the centers of cells, horizontally, vertically, or turning. The loop never crosses itself, branches off, or goes through the same cell twice.
• A rectangle, bordered by bold lines, is called a "room".
• Color each room blue or yellow.
• The loop must visit each room once, alternating between blue and yellow rooms.
• In a blue room, you must visit all of the moons and none of the suns; in a yellow room, you must visit all of the suns and none of the moons.