True, but I think slightly pedantic for this context. I think there have been proposed relational operators which produce the result you describe - a join, then

True, but I think slightly pedantic for this context. I think there have been proposed relational operators which produce the result you describe - a join, then remove the join key fields from the result. If we are in a pedantic mood, also, a relational-tuple is not exactly the same as a mathematical tuple, relational tuples take different forms depending on who's system you are following (e.g. whether the fields are ordered or not).