Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. In mathematics, there are usually many different ways to construct a topological tensor product of two topological vector spaces. For Hilbert spaces or nuclear spaces there is a simple well-behaved theory of tensor products (see Tensor product of Hilbert spaces), but for general Banach spaces or locally convex topological vector space the theory is notoriously subtle, and most mathematicians prefer to avoid it if possible.