Squares-in-Squares - Unicursal

Explanations

This is a so-called unicursal challenge. To prove whether it is possible or not, one should take a look at all the nodes in the shape. In order it is possible to draw without taking your pencil off the paper and without going over the same segment twice, at most TWO nodes can have ODD number of lines going into them. All of the rest nodes must have EVEN number of lines going into them.

As it can be seen all nodes in this shape have EVEN number of lines going into each of them. Thus, this shape is possible to be drawn without taking the pencil off the paper and without going over the same segment twice.

A basic solution is shown in the diagram.