Complex sentence: In the U.S., both LexisNexis and Westlaw offer free optional training seminars for law-school students, which supplement the mandatory training provided by law schools on how to perform traditional legal research in a law library.
Split into simpler sentences: In the U.S., both LexisNexis and Westlaw offer free optional training seminars for law-school students. These seminars supplement the mandatory training provided by law schools in how to perform traditional legal research in a law library.