Looking at the picture below (b) is described as an OR gate. I’m confused because with either threshold being met on the $$N_1$$ or $$N_2$$ neuron, with thresholds 1 and 2, there are not enough inputs to reach the threshold of 3 for $$N_3$$. So how is this an OR gate?
(c) makes sense because the sum of the input to $$N_3$$ is 3 when both $$N_1$$ and $$N_2$$ are at their thresholds.