Here's an invalid math proof that was considered valid for 59 years.
— Fermat's Library (@fermatslibrary) May 1, 2020
In 1923, Henri Dulac published an accepted solution for Hilbert's Problem 16-II, for which he was awarded several prizes. In 1982, Ilyashenko and Ecalle found a gap in the proof that was only filled in 1992. pic.twitter.com/qevhkyeG5z