# Substitute elementary symmetric functions in a polynomial

Suppose I do the following:

```
sage: SF=SymmetricFunctions(QQ)
sage: poly=SF.e()(SF.from_polynomial(x^2+y^2))
sage: poly
e[1, 1] - 2*e[2]
```

Now I would like to substitute `e[1, 1]`

in that expression. However:

```
sage: poly.subs({SF.e()[1, 1]: 1})
e[1, 1] - 2*e[2]
```

Does not do what I want (in fact it does not do anything). Is there a way to substitute a specific elementary polynomial?