I’ll try to explain, but that’s likely to reveal more misunderstandings on my part.
I was trying to compare symbolic expressions produced by the Symbolics package.
== appears to be produce a new symbolic expression. === seems to check for some sort of structural equivalence (which is sometimes, but not always, useful).
Maple has evalb which has semantics something like, “No really check if they are equal, don’t just create a new expression capturing the postulate that they are equal”.
I’m momentarily under the impression that isequals is like Maple’s evalb.