function command( pres ) {
	return onCommand;

	/**
	* Prints presentation help text.
	*
	* @private
	*/
	function onCommand() {
		pres._repl._ostream.write( HELP ); // eslint-disable-line no-underscore-dangle
	}
}
Returns a callback to be invoked upon calling the `pres` command.

@private
@param {Presentation} pres - presentation instance
@returns {Function} callback