Circuit that does not use the same arc twice.

### Example

In this directed graph, the circuit that passes, in order, through the arcs *a*, *b*, *c*, *d*, *e* and *n* is a simple circuit.

In this directed graph, the circuit that passes, in order, through the arcs *a*, *b*, *c*, *d*, *g*, *b*, *f* and *n* is a non-simple circuit.