\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}}}

$$f(x,y)=\cases
(x-2)+(y-2),&x\geqslant2\land y\geqslant 2,\cr
(x-2)-(y-2),&x\geqslant2\land y<2,\cr
-(x-2)+(y-2),&x<2\land y\geqslant 2,\cr
-(x-2)-(y-2),&x<2\land y<2.
\endcases$$
\bye