The National Gallery or Art’s “Jan Lievens: A Dutch Master Rediscovered” is all about pulling this often-overlooked 17th century master out of the shadow of his better-remembered contemporary, Rembrandt van Rijn. We asked the show’s curator, Arthur K. Wheelock, Jr., to point out a few of the Rembrandts in the Gallery’s collection that show a clear Lievens influence, rather than the other way around.