1-liners app for iPhone and iPad

Train your brain with this classical line-drawing puzzle! Trace the shapes by drawing each line once and only once. As you progress through the levels, things will become increasingly difficult, and you will no longer be allowed to cross already drawn lines. Only a true master of tracing can pass all 40 (as of version 1.3) levels!

A bit of history: known as The House of Santa Claus, this is an old German drawing game, originally intended for children. These drawings are also referred to as Euler paths, from the Swiss mathematician Leonhard Euler (1707-1783). Euler worked on the Konigsberg bridge problem, which concerned finding a tour around the city of Konigsberg, crossing all seven bridges in the city once and only once. Euler managed to find a set of rules to determine whether a graph can be traversed in one go or not. Now it is up to you to find your way through these paths and claim the title of Master Tracer!