Steps To Reproduce

We have

sage: R.<x,y> = QQ[]
sage: ((x+y)^3)[2,1]
3

but

sage: R.<x,y> = QQ[[]]
sage: ((x+y)^3)[2,1]
[...]
TypeError: unsupported operand parent(s) for <=: 'The Infinity Ring' and '<class 'tuple'>'

Expected Behavior

There should be a simple interface (including indexing via []) for accessing a particular coefficient of a power series, similarly to that of multivariate polynomials.

Actual Behavior

Functionality for accessing individual coefficients is missing.

Additional Information

No response

Environment

• OS: Ubuntu 24.04.1 LTS
• Sage Version: 10.6.beta1

Checklist

• I have searched the existing issues for a bug report that matches the one I want to file, without success.
• I have read the documentation and troubleshoot guide