I am preparing the application for an AP position at a local university. The documents I am required to submit include recommendation letters from three referees, who the university's website states should preferably be my ex-supervisor and/or employer. But altogether I have only two ex-supervisors in the past.
My question is, who could serve as an a alternative referee for me (other than ex-supervisor and employer)?
My understanding of the preference is someone who has worked with you for a relatively long period of time and therefore is in a position to speak on behalf of you. I had thought of my collaborators, but most of them work with me on a short-term. I have only one long-term collaborator, but he is from math dept. (I am an engineer).