The funniest example I know of is the number of conics tangent to five conics. There are now a number of different proofs, all based on modern intersection theory. Over the years, and until Fulton and Mcpherson formalized/discovered/invented intersection theory people gave several wrong answers, as well as several wrong proofs of the correct one.

The funniest example I know of is the number of conics tangent to five conics. There are now a number of different proofs, all based on modern intersection theory. Over the years, and until Fulton and MacPherson formalized/discovered/invented intersection theory people gave several wrong answers, as well as several wrong proofs of the correct one.