Let $H$ be the Hilbert space of square-integrable functions on the measure space of reals. Define $H \xrightarrow{s} \mathbf{C}$ by $\varsigma(\Omega)=\int_{\mathbf{R}} f e^{i k x} d \mu$, where $k$ is any number. This $\varsigma$ is apparently continuous and linear, and apparently not of the form $\varsigma(h)=(\underline{h}, h)$. What is wrong?