1 | initial version |

Figured it out myself.

My iteration starts with a graph of just one edge, then adds different types of edges to it. Initially, I had

```
G=Graph({0:[1],1:[]})
```

I checked in detail through the Sage manual pages on graphs, and found that there are options `multiedges`

and `loops`

that can be set for a given graph. So now I have

```
G=Graph(multiedges=True,loops=True)
G.add_edge(0,1)
```

This gives me exactly what I want. Now `G.add_edge(0,0)`

adds a loop to the graph, and `G.add_edge(0,1)`

makes it have a pair of multiple edges.

My problem was that Sage assumes `False`

values by default for these options, meaning that a graph by default is simple.

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