https://sites.google.com/site/howardwilliamsmith/publications-1
Among other things, it explains the research questions nicely. But here is the crucial part:
In the Summer of 2015 Pasquale and Stephan became concerned about the tension between the two papers, and asked for the two projects to be merged and for all four people involved to be made coauthors on both papers. I very much understood and sympathized with their disappointment that the substantial work they had put in on the planner paper had not resulted in a better outcome. I could also see the argument for regarding the two papers as belonging to a common project, although I preferred not to do this, especially since the paper with Oyvind was essentially finished. In any case, Oyvind did not want this, because he did not think Pasquale and Stephan had contributed to our paper. I agreed with this, as I still do, and therefore supported Oyvind’s decision.
Pasquale then told us that he would dispute the authorship of the paper with journal editors. Oyvind and I thought the worst outcome would be for the paper's publication to be delayed or prevented. In order not to risk this outcome, we agreed to Pasquale's and Stephan's demand of including them as authors.