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I am an undergraduate student volunteered at a research lab 2 years ago, working under a phd student. At the end of the work term, the phd student arranged a meeting with the prof so that I presented my work to him. He was rather impressed and promised to provide reference (2 years ago).
Right now, I am applying graduate studies so I would need his recommendation letter. But the problem is that he might not remember me because I didn't work directly under him and I merely gave a presentation. What kind of approach should I take in order to remind him of this issue?