This distinction has been called an "open exposition problem", versus an "open research problem". Once Freedman's proof was accepted, it was no longer an open

This distinction has been called an "open exposition problem", versus an "open research problem". Once Freedman's proof was accepted, it was no longer an open research problem; on the publication of this book, it will (hopefully) no longer be an open exposition problem. The phrase was coined by Timothy Chow in his paper A Beginner's Guide To Forcing [0]; > "All mathematicians are familiar with the concept of an open research problem. I propose the less familiar concept of an open exposition problem. Solving an open exposition problem means explaining a mathematical subject in a way that renders it totally perspicuous. Every step should be motivated and clear; ideally, students should feel that they could have arrived at the results themselves." [0] https://arxiv.org/abs/0712.1320 https://arxiv.org/abs/0712.1320