```python
In [0]: ff = Integral(x*y*z, (x, 1, 2), (y, 1, 3))

In [1]: ff.is_number
Out[0]: False

In [2]: ff.free_symbols
Out[1]: set([z])

In [3]: ff.atoms(Symbol)
Out[2]: set([x, y, z])
```
> Why do we need these tests?

This is to test whether ```free_symbols``` gets what is required and exclude bounded variables from being considered as ```isyms```.