usage: /usr/bin/eqn [-CNrR] [-d xy] [-f global-italic-font] [-m minimum-type-size] [-M eqnrc-directory] [-p super/subscript-size-reduction] [-s global-type-size] [-T device] [file ...]
usage: /usr/bin/eqn {-v | --version}
usage: /usr/bin/eqn --help

GNU eqn is a filter that translates expressions in its own language,
embedded in roff(7) input, into mathematical notation typeset by
GNU troff(1).  See the eqn(1) manual page.