### Adding elements to a set

I learned Python a long while ago before I decided to get into SageMath for mathematical purposes.

I am a bit puzzled that I don't seem to have a way to add an element to a set when using the SageMath definition 'Set()', but there seems to be no problem when doing this using the Python definition 'set()', namely:

```
a=2; b=3; c=4
D=Set([a,b])
D.add(c)
```

gives the error

```
'Set_object_enumerated_with_category' object has no attribute 'add'
```

whereas

```
a=2; b=3; c=4
D=set([a,b])
D.add(c)
```

gives no problem (notice the difference in capital letter when creating set).

I am using the following workaround

```
a=2; b=3; c=4
D=Set([a,b])
D=D.union(Set([c]))
```

but it seems rather artificial. Is there no more natural way to proceed? Is there a natural reason to explain why 'add' is not a method of 'Set'?