As a professor myself who has done this, if he's not dumb he wont. Unless you make it clear you want it in writing and also make it clear you are not doing it for grades in writing. Also don't communicate any of that until you are done with taking his class. Also make it clear to him that it will be private and not become a bigger deal campus thing. Check those boxes, understand their career is on the line, and be compassionate. Also dont do it if your prof is married or in a relationship.

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