When $$a\ne 0$$, there are two solutions to $$a^2x+bx+c=0$$ and they are $x=-b\pm {\sqrt{b^2-4ac}\over 2a}.$

We prove that the duality map $$\langle\,,\rangle:(\ell^\infty,\hbox{weak})\times((\ell^\infty)^*,\hbox{weak}^* )\to {\bf R}$$ is not Borel. More generally, the evaluation $$e:(C(K),\hbox{weak})\times K\to{\bf R}$$ , $$e(f,x) = f(x)$$, is not Borel for any function space $$C(K)$$ on a compact $$F$$-space. We also show that a non-coincidence of norm-Borel and weak-Borel sets in a function space does not imply that the duality map is non-Borel.