This is my code

```
m=[1,2,3,4]
c=[[1,3],[2,3],[1,2],[3,4]]
for i in Subsets(m):
print(i)
alpha_ij=0
for j in c:
delta_ij=set(i).symmetric_difference(set(j))
print(delta_ij)
for i in delta_ij:
alpha_ij=alpha_ij+2^i
print(alpha_ij)
```

When I compile it I get

```
{}
set([1, 3])
Traceback (most recent call last): for j in c:
File "", line 1, in <module>
File "/tmp/tmpgaYE70/___code___.py", line 10, in <module>
delta_ij=set(i).symmetric_difference(set(j))
TypeError: 'sage.rings.integer.Integer' object is not iterable
```

Which I do not understand because I do not think that I have iterated over any integer in any part of the code. The problem seem to be the last three lines because if delete them and compile the code there does not appear any error.