To keep a book or discard it?

I own more books than I can read in a lifetime. I need to try out Erik Knutzen's system for cleaning his bookshelves. 

 The book was released to the universe if: 

-- I had read it and absorbed the information 
-- The library has a copy 
--  It does not give me joy 
-- I don’t think I’ll ever read it 
-- My interests have changed 
--I read part but don’t think I’ll read the rest 

I kept the book if: 

-- It’s a volume I refer to for reference on a regular basis 
-- It gives me joy 
-- It’s especially beautiful as an object (only one or two books actually      ended up in this category — I’m not a book collector) 
-- I really intend to read it I want to re-read it

Watercolor and Gouache on paper by Pia Mileaf, Age 11
Found in Art Within Reach - From the WPA to the Present, published in 2010 by The Children's Museum of the Arts, New York City