\input amstex
\font\amssy=msam10

\def\leqslant{\mathrel{\hbox{\amssy\char54}}}
\def\geqslant{\mathrel{\hbox{\amssy\char62}}}

$\exists\varepsilon>0\ \forall n_0\in\hbox{\pmb N}\ \exists n\in\hbox{\pmb N}\quad n>n_0\land|a_n-a|\geqslant\varepsilon$
\bye