Guide
How to solve any one-line puzzle
The two-odd-dots rule from 1736, and where to start.
Every one-line figure follows a rule Leonhard Euler found in 1736. Count how many lines meet at each dot.
If exactly two dots have an odd count, start at one of them: you will finish at the other. If every dot is even, start anywhere and you will end where you began. If more than two are odd, the figure cannot be drawn in one stroke, which is why every Neo Puzzles level has zero or two.
Save bridges for last: before you cross a line that is the only link to an unfinished part, finish that part first.