Solution
= Solution
\b[False.] Take $f(s,t)=s$. Then $s^{2n}t^{2m}f(s,t)$ is odd in $s$, so every stated integral over $[-1,1]^2$ vanishes, although $f$ is not zero.
= Solution
\b[False.] Take $f(s,t)=s$. Then $s^{2n}t^{2m}f(s,t)$ is odd in $s$, so every stated integral over $[-1,1]^2$ vanishes, although $f$ is not zero.