 taking two things of the same type and returning the same type. But as you saw in the previous section, a magma isn't enough to describe something that's appendable because subtraction is a magma, and subtraction <i>doesn't combine</i> or add two things together, it takes something away.</p><p>What's really needed is a magma that satisfies two <i>laws</i> in order to truly describe something that's appendable:</p><ul><li><p>The <a href="https://en.m.wikipedia.org/wiki/Associative_property">Law of Associati