You're right but I'm just making the point that machine arithmetic ain't number arithmetic and you can't rearrange freely. His example included SUM(b + c) and

You're right but I'm just making the point that machine arithmetic ain't number arithmetic and you can't rearrange freely. His example included SUM(b + c) and SUM(c + b) as equivalent. As such it probably is[1] but extend it to 3 numbers and you can't rearrange, as I think we agree. [1] assuming b and c are numbers not strings, as + is string concat in some dialects