SPRINGFIELD, Ill. (AP) _ A law-book used by Abraham Lincoln has been reunited with a partner edition at the Abraham Lincoln Presidential Library and Museum.

Officials say the book is the second of a three-volume set called “A Treatise on the Law of Evidence” by Simon Greenleaf. The library and museum own the first volume. The whereabouts of the third remain a mystery.

The Montana Historical Society donated the book. It obtained it in 1927 from a Helena resident whose father had bought it years earlier.

The book is signed “Lincoln & Herndon” in the hand of Lincoln’s law partner, William Herndon. The firm, which later changed its name, closed in 1909.

Officials say Lincoln considered “Treatise” important, listing it as a must-read in two surviving letters to aspiring attorneys.