Draw lines along grid edges so as to divide the grid up into connected regions of squares.
Every region should have two-way rotational symmetry, should contain exactly one dot which is in its center, and should contain no lines separating two of its own squares from each other. A region satisfying all of these requirements will be automatically highlighted.
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).
Click a grid edge to add or remove a line. Press on a grid edge and drag along the grid to do the same to every edge you pass over that looked the same as the first.
With the keyboard, the arrow keys move a cursor around the board. Enter or Space does what a click does to the grid edge under it.
Drag from a dot into a grid square to place an arrow there pointing back at the dot, to indicate that you think that square must belong in the same region as that dot. The square opposite the dot gets the matching arrow at the same time, because a region is symmetric about its dot. Drag an existing arrow to move it, or drop it off the edge of the grid to remove it.
You can also drag the other way round: start inside an empty square, away from its edges, and drag towards a dot, and the arrow is placed when you let go. While you do, every dot that square could legally belong to is ringed, and the one you are aiming at is ringed more heavily. If you would rather work that out for yourself, turn off While dragging from a cell, ring the dots it could belong to in Preferences — the gesture keeps working, without the rings.
Either mouse button will do, and on a touchscreen an ordinary finger drag works. The keyboard can drag too: on a dot, an arrow or an empty square, Enter or Space starts the drag, the arrow keys steer it, and Enter or Space again finishes it.
Hint explains the next step rather than simply making it. Most of what it says is about the arrows. The square opposite the dot, which the hint calls its partner, gets its arrow at the same time, as always, so it is ringed once rather than twice: it comes along rather than being what the hint is telling you about. The marks it reasons from are drawn in a second color, so you can see the reason as well as read it. None of these marks is a fill: a square’s color is the dot it belongs to, which is exactly what the hint is reasoning about.
One of the things it looks for is the same thing the drag rings show you: when only one dot could possibly own a square, because no galaxy around any other dot can stretch to it, that square is settled, and dragging from it will ring exactly one dot. Another dot is ruled out when the square opposite it would be off the board or on top of a dot, when other dots cut the square off from it, or when either square already lies in a finished galaxy.
Once two neighboring squares are settled on different dots, the hint asks for the line between them, and it is those lines, not the arrows, that finish the puzzle.
Every hint is a deduction you could have made from what is on the board. On an Unreasonable board there may come a point where no deduction is left and the only way on is to try something and see whether it works — that is what the difficulty name means. The hint says so rather than guessing for you: save your position, try it, and undo if it breaks. (Or use Solve, if you would rather see the answer.)
A hint is refused while anything on the board contradicts the solution. The offending squares and lines light up instead, exactly as they do for Check & save.
These parameters are available from the ‘Custom type…’ option on the ‘Type’ menu.