### Simple question on displaying summation

Hi,

I'm defining a few summation functions for displaying and evaluating later, but I don't understand how to do it.

So, I'm looking at the basic Sage Quick Reference and I see under Arithmetic:
sum(f(i) for i in (k..n))

But when I try to make it symbolic to show, like something simple like this:

```
var('i,n')
f(n)=sum(i for i in (0..n))
show(f)
```

But then I get

```
TypeError: unable to simplify to float approximation
```

Which makes me think its trying to evaluate the sum rather than make it a symbolic expression. Then I ran across "symbolic_sum" somewhere, but I can't find any documentation about it now...

Any suggestions?

Erik