Addition and Expansion What is Addition Two ideas with one being an addition to the other can be combined together by indicators of addition. There are two types of addition,one is reinforcement,the other is equation.Since it is often difficult to tell them apart.We here treat them together. Writing ClassWriting Class Addition and Expansion What is Addition ? Two ideas with one being an addition to the other can be combined together by indicators of addition. There are two types of addition, one is reinforcement, the other is equation. Since it is often difficult to tell them apart. We here treat them together