### Why does expand-simplify break print_latex_func?

Here's a minimal example of what I am talking about. Both print statements should return the same output in this scenario.

```
,var n x
def my_latex_print(self, *args):
return "a_{%s}" %(', '.join(map(latex, args)))
a=function('a',nargs=1,print_latex_func=my_latex_print)(n)
sexp=a(n=n+1)+a(n=n)
print latex(sexp)
sexp=simplify(expand(sexp))
print latex(sexp)
```

However, the outputs differ:

```
a_{n + 1} + a_{n}
a\left(n + 1\right) + a\left(n\right)
```

Of course simplify-expand may lead to a different expression, but that's not what I am concerned about. I am concerned about the representation of `a(n)`

instead of `a_n`

in the output.

My main question is: How can I recover `a_n`

out of `sexp`

at the end of my code?