# If the weak limit is zero, is it true that the sequence of functions tends to zero almost everywhere?

Assume that a sequence of continuous functions $(f_n)$, where $f:[0,1]\to\mathbb{R}$ has the following property. For any smooth function $\phi:[0,1]\to\mathbb{R}$ one has $$\lim_{n\to\infty } \int_0^1\phi(x) f_n(x)\,dx\to0.$$

Is it true that $f_n(x)\to 0$ for almost all $x\in[0,1]$.

Note that it is not assumed here that $f_n$ are bounded or positive

• Look up the Riemann Lebesgue lemma. – copper.hat Aug 2 '18 at 17:42
• thanks! that was very helpful – Oleg Aug 2 '18 at 17:46

No. $f_n(x)=\sin(nx)$ is a counterexample.