A space with an inner product but is not Hilbert
14516
The space of continuous functions $C([0,1])$ is not complete in the $L^2$ norm
57310
Prove $\mathbb{Z}$ is not a vector space over a field
39114
Prove that a set in $\mathbb R^3$ is not an algebraic set
67383
Prove that $G'$ is not planar.
69893
An inner product space and its proper closed subspace with trivial orthogonal complement
4717
The union of linear subspaces is not necessarily a subspace
90826
Constructing a subset not in $\mathcal{B}(\mathbb{R})$ explicitly
98391
example of a nonempty subset is closed under scalar multiplication but not a subspace
102914
Integral domain that is not a factorization domain
92281
Normal Operator that is not Self-Adjoint
17378
Characterize finite dimensional algebras without nilpotent elements
152196
About inner products, norms and metrics
129020
Problem with the Definition of Inner Product Space.
70861
$\mathbb P^n\times \mathbb P^m\not\cong \mathbb P^{m+n}$
140835
Inner Product Space Inequality
11259
Prove $R\times S$ is not an integral domain
1475
In an incomplete inner product space, is a closed linear subspace equal to the orthogonal complement of its orthogonal complement?