Relational algebra : Parenthesis issue

Question

I have been given this homework on relational algebra.

I am having trouble figuring what differs between both relation instances as the parenthesis are placed otherwise in the second case. I would say that both return the same result but I don't think it is the case.

If anyone could provide an explanation that would be nice ! Thank you

Answer 1

Looks like the second variant is an error. The outer projection looks for sname but is only passed sid.