NIB

Level 01 · Two Ends. Nine nodes, twelve lines, nothing dangling. Only two nodes carry an odd count, and they are the only places the line may begin and end.

1. 01Tap any node to put the nib down. Tap a neighbour to draw the line between them.
2. 02Every line must be drawn exactly once, and the nib is never lifted off the paper.
3. 03ODD counts the nodes with an odd number of undrawn lines. It may never rise above two.