I have difficulties on translating the sentence "numerus qui est minor quam nullus". What's the English translation of this?
Cum subrahitur numerus naturalis de alio naturali,
When a natural number is subtracted from another natural (number),
exsultat interdum non naturalis sed ...
there sometimes results not a natural number but...
...sed numerus qui est minor quam nullus.
but a number which is less than zero.
The concept of zero reached Baghdad by 773 AD and appears in book Liber Abaci, or “Abacus book,” by Fibonacci in 1202