You would usually use something like \hookrightarrow instead. The set is isomorphic to a subset. In the same way the real line is "included" in the plane (\R \

You would usually use something like \hookrightarrow instead. The set is isomorphic to a subset. In the same way the real line is "included" in the plane (\R \times \{0\}) or the sphere is not only a subset of the whole space but a submanifold. Math uses lots of polymorphism and overloaded notation, but that is also part of the beauty, where "A=A" can actually be a deep result about concepts being compatible.