Jamieson, Fausset and Brown on Ruth 4:9

Ru 4:9-12. He Marries Ruth.

9. Boaz said unto the elders, Ye are witnesses this day, that I have bought all that was ... Chilion's and Mahlon's, of the hand of Naomi--Although the widow of Chilion was still living, no regard was paid to her in the disposal of her husband's property. From her remaining in Moab, she was considered to have either been married again, or to have renounced all right to an inheritance with the family of Elimelech.