> All of those definitions are interrelated, and collectively they define what it means to be a number. There is nothing informal about it. Then you could simp

> All of those definitions are interrelated, and collectively they define what it means to be a number. There is nothing informal about it. Then you could simply point to the formalism which unites various mathematical activity under some universal model of number. I will reiterate the claim again — "number" is an informal concept among mathematicians and they are fine with that.