# Error in calling a custom function from sage

I used this guide to add module containing some utility to the sage.

My module (`myfunc.py`

) looks like this:

```
def perm(n, r):
return factorial(n)/factorial(n-r)
def comb(n, r):
return perm(n, r)/factorial(r)
```

To import the module I use the following `import`

statement:

```
sage: from myfunc import perm
```

So far so good.

When I call the `perm()`

or `comb()`

function. I get the following error:

```
1 def perm(n, r):
----> 2 return factorial(n)/factorial(n-r)
3
4 def comb(n, r):
5 return perm(n, r)/factorial(r)
NameError: name 'factorial' is not defined
```