In a paper published recently in a math journal, the main result is presented as being new, but in fact it is not new, and I'm sure that the authors knew this before submitting the paper. I have informed the journal editor who handled this paper, who told me he would forward my message to the managing editor. I have not heard anything since then. What else can (or should) I do?
For what it's worth, I am a tenured professor.
In more detail, there was a previous paper [A] which proved a certain result (1). The proof given in [A] actually proves a stronger result (2) which has a messy statement, and notes that (2) implies (1) (where (1) has a simple statement). The main result (3) of the recent paper [B] implies (1), but is implied by (2). Moreover, the proof in [B] is identical to the proof in [A] (and the authors of [B] say this in their paper), except that the proof in [B] uses a stronger auxiliary result at one step. So the authors of [B] must have been aware of the stronger result (2) proved in [A], but they do not mention (2) in their paper, and certainly do not mention that their main result follows immediately from (2). To me, this shows that the authors of [B] published their paper under false pretenses, by intentionally misrepresenting prior work. In addition, the auxiliary result mentioned above is presented as a new result in [B], even though it has been published several times and also the authors of [B] were fully aware of this fact, since they had written previous papers citing an essentially identical result from a paper [C]. Even beyond this, the paper [C] contains a result which is stronger than (1), (2), or (3), although the authors of [B] do not mention this.
If people think I am overreacting, I would be happy to hear this. It's possible that my views of proper academic behavior are not standard ones. I don't have a fully articulated philosophy about these things, I just feel like the authors did something wrong and should not benefit from doing it.
Added later: The situation has been resolved. The journal's editor informed me that, after inspecting the documentation I sent him, he has decided to require the authors to withdraw their paper from the journal. I don't know the logistics of this, but to me it seems like the appropriate outcome.