Hey folks,

I’m trying to subtract one graph from another and I’m getting results I wouldn’t expect. I’m creating a graph, finding a subcomponent, creating a subgraph, then subtracting the subgraph from the initial graph. igraph seems to be cutting the wrong edges. Could someone help me understand what’s going on? (all graphs are shown at the end. The forum limits the number of images new users can upload to 1.)

```
import igraph
g= igraph.Graph(directed=True)
g.add_vertices(["A","B","C","BA","BB","BC","CA","CAA"])
g.add_edges([["A","B"], ["A","C"],["B","BA"],["B","BB"], ["B","BC"],["C","CA"],["CA","CAA"]])
print(g)
layt = g.layout_reingold_tilford(mode="out", root=rn.indices)
igraph.plot(g, layout=layt, vertex_label=g.vs["name"],
)
```

I see the graph in Figure 1 below, which I expected

```
sub = g.subcomponent("C", "out")
print(sub)
# sub_names = g.vs.
# sub_names = [g.vs[i]["name"] for i in sub]
sub = g.subgraph(sub)
sublayt = sub.layout_reingold_tilford(mode="out", root=[0])
igraph.plot(sub, layout=sublayt, vertex_label=sub.vs["name"])
```

I see the graph in Figure 2 below, which I expected.

```
subtracted = g.copy()
subtracted = subtracted - sub
subtractedlayt = subtracted.layout_reingold_tilford(mode="out", root=[0])
igraph.plot(subtracted, layout=subtractedlayt, vertex_label=subtracted.vs["name"])
```

I see the graph in Figure 3 below, which I did *not* expect. Shouldn’t the operation have just removed the C/CA/CAA subgraph from the first one? What am I missing here?