Can you help explain something? This course teaches "llur" instead of what I've heard before: "seu." I know that "seu" is singular, but I've heard it for plural. I also know there are regional variations in Catalán, but is "llur" used today somewhere? Thank you! Ex: Ells llegeixen els llurs llibres. (I may have made a mistake in this example, because I'm trying to remember how it was written.)