That part I get (I think). I’m just reading f(x) = 0 as a system of 1 linear equation with 2 variables, which in my understanding is represented by a 1x2 matrix mapping \mathbb{R}^2 to \mathbb{R}^1. And isn’t the element of \mathbb{R}^0 an empty (column) vector like B? Not great at math so I might be misremembering stuff.