#!/bin/sh

# science speak from wikipedia
! eq $# 2 && printf "Usage: $0 [minuend] [subtrahend]\n" >/dev/stderr && exit 1

! stris int "$1" && printf "$0: $1: Not an integer\n" >/dev/stderr && exit 1
! stris int "$2" && printf "$0: $2: Not an integer\n" >/dev/stderr && exit 1

minuend=$1
subtrahend=$2

# (- a b) == (+ a (* b -1))
printf "%b\n" $(add $minuend $(multiply $subtrahend -1))
exit 0