How to cite a previous single-author paper by oneself? Suppose my name is John Smith, and I am writing a new (single-author) paper which wants to cite a previous (single-author) work by myself.

What is the best style for this?

(1) As we showed in [1], the following condition applies ....

(2) As I showed in [1], the following condition applies ....

(3) As Smith showed in [1], the following condition applies ....

(4) As [1] shows, the following condition applies ....

I would prefer to avoid (4) because it is easier for the reader to follow a discussion where names (rather than numbers) are associated with certain concepts. This leads me to prefer (3), because a specific name is attached. 

The problem with (1) is that it can be difficult for the reader to distinguish two meanings of "we" in the context of a (math) paper: first, there is the impersonal use of we as in "we define a group as a set with an operation + etc.", and second there is the use of we as in the actual human writing the paper.

The problem with (2) is that it draws attention to myself as opposed to my ideas, which is the opposite of what I'd like in a scholarly paper

Does it matter if this is in the middle of a paragraph citing a wide variety of authors, only some of whom happen to be equal to myself? For example, 
"As Jones showed in [2], ...., As Doe showed in [3], ...., As Smith (or we) or (I) showed in [1], .... "
In my field of psychology, it is normal to treat any previous citation as if it was another person. In a sense it is the article that presents the point. This convention is also related to the use of double blind review in many journals.

So you'd just write: 


  Smith (2015) showed that ...


or


  Smith (2015) conducted a study and found that ...