Grades K - 3. Level M-O. From the author and illustrator duo of the best-selling Words Are CATegorical® series, Math Is CATegorical® introduces basic math concepts for young readers and reveals that sometimes math is easier to show than explain! Pairing clever rhyming verse with comical cartoon cats, Brian P. Cleary and Brian Gable help children add up just how fun math can be! Set of 9 books.