"Sac" in French is spelled as "s-a-c."
un cartable
dans mon sac
sac de bonbons
"Book" in French is spelled "livre."
Bolsa de libros is "book bag"; you can also put your books in a mochila, a knapsack/backpack.
a book is spelled 'un livre' in French.
The spell diffindo splits seams and bindings (spine in a book, bottom of a bag)
un cahier d'exercices
une livre
regardez le livre
In the fourth book, Harry used the spell, Diffindo, to rip Cedric Diggory.