Leduc and Beauvoir
The screenplay made the relationship between these two probably more central and important than it really was to either of them, but that was a smart move in structuring a story about a complex and messy life (Leduc's), contrasting with a glamorous, successful one (De Beauvoir's). The relationship between them here is really intriguing: Leduc is the practitioner, and Beauvoir the theorist, and each one needs the other for completion.
The screenplay simplifies both women a great deal, but it's in the interests of telling a good, well-paced story, almost a parable about writing, thinking, and the "second sex." Beauvoir is made to seem more icy and aloof than she really was--according to other people's memoirs of her, anyway. But then, maybe being icy and aloof was the best way to handle someone as desperate and volatile as Leduc. Both performances were excellent.