Researchers have reunited two pieces of the earliest known document by Abraham Lincoln. It’s math homework, and part of it’s at the University of Chicago.

For years, the document was just a fragment of a page on which a teenage Lincoln worked out his math projects.

Then Daniel Stowell started looking at a scanned image. Stowell’s the editor of Lincoln’s papers at the Abraham Lincoln Presidential Library in Springfield. Stowell thought it might fit with another fragment from Brown University. He says the discovery was thrilling.

STOWELL: It gives you an insight into Lincoln the teen-ager becoming Lincoln the young man, becoming Lincoln the leader and president we know.

Lincoln’s stepmother gave the math copybook to one of Lincoln’s law partners after his death. The law partner ripped it up and gave pages to friends.