They didn't have modern notation, specifically the integers as a convention hadn't been adopted by primarily Greek mathematicians like Diophantus. That is very

They didn't have modern notation, specifically the integers as a convention hadn't been adopted by primarily Greek mathematicians like Diophantus. That is very different from understanding concepts like owing someone money, which is a form of negative. Chinese and Indian mathematicians and accounting from Babylonian times didn't have the same mental blocks. The Bakhshali manuscript is still the first known example of modernish notation I think, but used +