What a disappointment here. It's my fault, I had not seen it contained only 38 pages. I had no idea that it would only deal with certain ideas, addressed very quickly: we fly over, barely. If one starts, it does not get us too. Very useful for primary though. The syntax is absolutely devastating, I have never seen that in a written published, commas are added as random phrases, making everything very unpleasant to read. In short, I think it is better to keep its 5 or 6 and put them in another book, bigger, more detailed, more complete, but especially: better written.