\input amstex
\font\amssy=msam10

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

\def\eqslantless{\mathrel{\hbox{\amssy\char48}}}
\def\eqslantgtr{\mathrel{\hbox{\amssy\char49}}}

$$\pmb{\mathrm{R}}^+_0=\{x\in\pmb{\mathrm{R}}\mid x\geqslant0\}$$
\bye