Thanks for the clarification. I now understand the main goal of the examples. I was confused by the remarks in the example "(other possibilities will be excluded for lack of join clauses)" as this is not a true statement: some possibilities are not shown for lack of join clauses while others are not shown for the sake of simplicity. I think it would be nice to add what you explained somewhere in the text to indicate this is a partial example with the main goal of illustrating join rels that have no linking clauses are not considered by the optimizer; I got the impression that these two examples are to illustrate how DP works in the optimizer.
You're right that these examples do not consider the effects of clauses generated by the EquivalenceClass machinery. But I don't think the exposition would be improved by mentioning that here. The point of these examples is that we don't consider joining rels that have no linking clauses at all.
We could possibly avoid the inaccuracy by making the examples use some other operators that are not equijoins. But I wonder if that would not be more confusing rather than less so.
