publications - Citing a result due to a single author that appears in a paper with multiple authors

Let's say that Jones and Smith publish a mathematical paper containing a result (Theorem 3.1, say,) which is said in that paper to be due to Smith alone but appears for the first time in her joint paper with Jones. How should I cite this result?

Here are a few examples of ways I might cite the result if Jones were not a co-author of the paper (for definiteness let's say the paper is number 7 in my bibliography):

1. 
   

   "By a theorem of Smith [7, Theorem 3.1]..."

   
   


2. 
   

   "Our argument is based on that of Smith [7, Theorem 3.1]..."

   
   
   


3. 
   

   "...implies the hypothesis of Smith's theorem [7, Theorem 3.1]..."

   
   

How might I adapt these phrasings to the situation described above?

Answer

I would just cite it as "Jones and Smith" and not worry about it. The standard in math is to cite papers by their authors. If Smith wanted to be cited alone, she should have published the result herself.

I think this situation has some precedent in other fields. I might be wrong, but think some journals such as Nature (see http://www.nature.com/nature/authors/gta/#a5.5 "author contributions") make the authors disclose who did what. It does not mean that the paper needs to be cited differently depending on what part of it is used.