Kindergarten-Grade 4 The author has used the format of his popular Words are Categorical books (Millbrook) to look at mathematical functions. Subtraction is explained in rhyming text and simple, silly cartoons with excellent examples that range from angry bulldogs, hornets, and bowling pins to pieces of birthday cake, sports time-outs, and stuffed animals. The text is actually a rap that would be fun for students to memorize and perform. The illustrations are colorful and attractive, and an explanation of the equals sign is included. Despite a bit of filler at the end, this book has value in the mathematic section of libraries and will find a place in classrooms with teachers who want to appeal to a variety of learning styles.