I am refereeing a paper (a good one) for a mathematical journal. The author repeatedly writes like this: "we can't do", "we don't know" etc. He is not a native English speaker, and this paper is his first paper in English.
Question. I am going to ask the author to change "can't" and "don't" to more formal "cannot" and "do not". Is that a right thing to do?
I am not a native English speaker either....
(Since a referee is supposed not to disclose their identity, I ask the question anonymously.)