What are the effects of allowing students take one paper, say of A4 size, full of whatever they want, into an exam? It might be called a cheat sheet or something similar. Students might write it by hand, they might copy one from someone else, they might use $LaTeX$, etc. Anything goes.
I have taken such an exam twice in physics studies, but would be interested in the experiences of people who have assigned such exams, and literature on the subject, if any.
I am particularly interested in university-level mathematics courses, which probably include proofs and maybe calculations.