I am not a origami hobbyist myself and I was hoping that you could help me find a book for my brother who likes folding origami.
The book should not be too easy. He is mathematically gifted and I am looking for something that will challenge his mind. I don't know how difficult models he can actually fold. I bought him some time ago Origami for the Connoisseur and he folded that amazing beetle. It looks pretty difficult to me.

All suggestions are very much appreciated! Thanks already!
