Currently "Group(exprlist, P)" and "Aggregation(exprlist, func, scalarvals, Grp)" are presented and used as if they are independent operators of the algebraic syntax. For instance, they have their own cases/definitions for the eval function (see Evaluation of Group and Evaluation of Aggregation). Yet, they are not. Instead, they can only be used within the context of the 'AggregateJoin' operator.

In this sense, 'Group' and 'Aggregation' should become part of the definition of the 'AggregateJoin' operator in the algebraic syntax, instead of being present as independent operators.

Similarly, they should also not be covered directly as cases of the definition of the eval function. Doing so is formally incorrect because, for these two cases, the result is of a completely different kind than for any other case of the eval function.