Tap a square to shade it.
Shaded numbers in each row must add up to the goal on the right;
each column to the goal below.
Tap a shaded square again to ✕ it out
(a note to yourself — it doesn't count). Tap once more to clear.
Master mode: tap once for green (adds the number),
twice for red (subtracts it),
three times to ✕ it out. Goals can be negative.