Brahmasphutasiddhanta XVIII.22 (628 CE) gives the multiplication rule for signed numbers: negative × negative = positive, negative × positive = negative, positive × positive = positive. The conceptually hard half — negative times negative equals positive — would not be accepted in European mathematics until John Wallis (1685) at the earliest, and some historians argue not fully until Hankel (1867). Brahmagupta states it matter-of-factly, 1,057 years before Wallis.