Bribe

First panel: Two friends are in conversation. One has a bag of money in hand. The other says, "What's that bag of money for?" "Bribing a mathematician." "Uh...let me give you some advice..." Second panel (later): The person no longer has the bag of money anymore, and approaches the mathematician. He says, "I have a paper that needs a coauthor, but I require a favour--" She interjects, "Done!"