Slitherlink

1. 1Join neighbouring dots with lines to make one single closed loop. It never crosses itself and never branches.
2. 2A number in a square says how many of its four sides the loop uses. Squares without a number can have any number of sides used.
3. 3Tap between two dots to draw a line, tap again for a cross (a reminder that the loop does not go there), a third time to clear.
4. 4Start with the 0s: none of their sides is used, so cross them all. Two 3s side by side share a line between them. At every dot, the loop arrives and leaves: a dot has 0 or 2 lines, never 1 or 3.
5. 5Check my work marks the lines and crosses that are wrong. A hint settles one side: it costs a little XP, never time.
6. 6There is a new puzzle every day, the same for everyone: 5 by 5 from Sunday to Tuesday, 7 by 7 from Wednesday to Friday, 10 by 10 on Saturday. Every puzzle has one solution and can be solved by logic alone.

Keyboard: arrows move between dots, Shift and an arrow draws a line from the dot (again for a cross, again to clear), U to undo.