This article presents a research apparatus for investigating and making sense of stories that emerge from feedback that mathematicians provide on students' proofs. Using the commognitive framework, the notion of "didactical discourse on proof" is developed as a lens for conceptualizing mathematicians' practice of feedback provision. The notion is accompanied by a tentative organizational frame, within which didacticians and mathematicians can operate as partners. The methodological affordances of this apparatus are illustrated with a case study of a research topologist, who taught a small, graduate course in topology. The emerged characteristics of her feedback and discourse are situated in the literature and used to sketch future research avenues.