\input amstex
\def\sN{\bold{N}}
\def\sR{\bold{R}}
$$\biggl\{(m, n)\biggm|m,n\in\sN\land\sum\limits\Bigl\{x\in\sR\Bigm|\lfloor x\rfloor=m\{nx\}\Bigr\}=22\biggr\}$$