Are the Hardy-Littlewood “rules” unethical? For the second time recently, someone mentioned to me the Hardy-Littlewood rules for collaboration (and on that very site). From what I read about it, they include the following rule:


  And, finally, the fourth, and perhaps most important axiom, stated that it was quite indifferent if one of them had not contributed the least bit to the contents of a paper under their common name


How is it ethical to be a co-author of a paper you have “not contributed the least bit to”?

I was flummoxed when I read that, it would be considered a serious breach of ethics in the communities I know. Is that a practice (those “rules”) specific to mathematics? Or are they just not used any more?
I've always interpreted such remarks as meaning that the individual papers were just progress reports on their larger enterprise, to which both made irreplaceable contributions, and that they had no interest in keeping track of moment-by-moment relative contributions.

In particular, "on average", there was no misattribution or false credit.

(Further, the "not contributed the least" may easily be hyperbole, just to make the point.)

For that matter, if one is in regular correspondence with another, how to attribute ideas that develop gradually? I think their solution was entirely reasonable.