Hi PF! I am about to submit a publication, but as of now I think I am listed as second author (the only authors on this paper are my adviser and me). Is there a substantial difference between second author vs. co-author? Also, my adviser wrote the majority of the manuscript, though I wrote some and contributed to some analytical results that were missing. We together had a lot of conversations where we both helped the other. I wrote all the numerical code without help, I wrote all code for data processing (image processed data), and I conducted all experiments. Without me, there would not be any data. Processing this data was incredibly time-consuming and very complex, requiring strong math background. Given this, is it wrong for me to request co-author here?