.6 XOR solution after Goodfellow et al. (2016). There are three ReLU units, in two layers; we've called them h 1 , h 2 (h for "hidden layer") and y 1 . As before, the numbers on the arrows represent the weights w for each unit, and we represent the bias b as a weight on a unit clamped to +1, with the bias weights/units in gray.