nerd alert: krugman and the primacy of a concept

Paul Krugman writes:

It wasn’t until the Arabs invented Arabic numerals that the liquidity trap became a possibility.

Very erudite, very intellectual, very historically astute. But is it true? The liquidity trap describes a point at which a central bank’s infusion of cash into an economy fails to stimulate the economy because returns are already so low that people prefer to hoard cash. (Feel free to elaborate on, or correct, my amateurish description.) I’m very happy with the idea that the concept of zero has to predate economic behavior that worries about (sub)zero returns, but I would have thought economists would think it’s the actual existence of zero, not the concept of it, that drives the liquidity trap.