You’re given a grid that has been divided into areas, containing arrows and one or more goals (represented by circles). Your goal is to fill every empty space with an arrow pointing up, down, left or right while following these rules:
On a touch screen, a tap does what a click does, and a long press what a right-click does (more ways to right-click). A key the puzzle’s controls show as a button can be pressed there instead of on a keyboard.
Click and hold a square, then drag in one of the four directions to place an arrow. Or tap a square to select it and press one of the four arrow buttons below the grid, which is the same thing without the drag; the Clear button empties the selected square. Tapping a square that already holds an arrow of yours clears it instead of selecting it.
Right-click and drag to place a pencil mark, or press the Marks button below the grid to make ordinary drags — and the arrow buttons — leave marks until you press it again. A right-click without a drag does the same as the Marks button and selects the square, as it does in the other note-taking puzzles. The selected square is shaded while the buttons enter arrows, and shows a small triangle in its corner while they enter marks. A pencil appears in the top right corner while it is on. Pencil mode is sticky: once a right-click switches it on, it stays on wherever you click, until you right-click again. The Marks key is lit while it is on, and pressing the key also switches it. To have it last only until your next click, turn off Right-click toggles a sticky pencil mode (stays on until right-clicked again) in the preferences.
Press Fill marks among the puzzle’s controls to write in every pencil mark wherever nothing is placed and no mark is written yet. The M key does the same, on any board where M is not something you type. Marks you have narrowed are left alone, and pressing again never starts over: see Filling in all the pencil marks. A mark records an arrow you think a square could still hold, so a square’s marks are the arrows the grid’s edges leave open, and once every empty square has marks the press crosses off the ones each square’s own area has already used. Check & save treats a square whose marks have ruled out its answer as a mistake, in the same way it treats a wrong arrow.
Squares whose arrows already lead to a goal are shaded, so you can see how much of the grid is settled. A second preference shades squares caught in a loop instead, which can never reach a goal; it is off by default. Both are in the game’s preferences.
The keyboard can also be used. Move the cursor with the arrow keys, and press Enter followed with an arrow key to place an arrow. Use Space to add pencil marks. A question mark shows in the square while it waits for the arrow key. Alternatively, type 8, 2, 4 or 6 to enter the arrow that key points to on a numpad directly; the digits on the number row do the same.
This type was invented by Nikoli, who name it Roma.
More information: http://www.janko.at/Raetsel/Nikoli/Roma.htm
Hint explains the next step rather than simply making it. It works from your arrows and your pencil marks, so as long as no arrow is wrong and no square’s marks have crossed out its answer, it carries on from wherever you are; otherwise it asks you to fix the highlighted mistakes first. A square with no marks counts as holding every arrow its area hasn’t used yet that doesn’t point off the board, and the hint pencils marks in only when a step needs them. If you would rather it start from a fully marked grid, set Hints pencil in to Every candidate first in the preferences: it then begins by pressing Mark all twice, just as you would.
A few ideas are worth learning by name:
These parameters are available from the ‘Custom type…’ option on the ‘Type’ menu.