When I was growing up ( I was born in 1968) my mother had a set of World Book Encyclopedias and on the same set of shelves she had this boxed set of four : grey with red/maroon lettering . I could be wrong but I recall all four of the books having nursery rhymes/poems e.g. Jack Spratt, Old Mother Hubbard, Itsy bitsy spider, there was one about black birds baked in a pie. There was even one about a purple cow and the last line of it was I’d rather see than be one – and on the top of the page was what you could tell was a color picture of a Holstein cow but they had mad it look purple. The quality of the books were the same as the encyclopedias- hard shell, thick feel of the paper. I loved those books. I have a co-worker who also remembers the same set of books but her mother also did not keep them to her dismay and she and I both have been trying to figure out who published them and could you still find a set. There were tons of poems/ rhymes and I loved them all but the purple cow was my all time favorite. Any assistance would be greatly appreciated .