P E R C E P T R O N
            1958

  x1 ●──w1──┐
            │
  x2 ●──w2──┼──▶ ( Σ + b ) ──▶ ⟦ θ ⟧ ──▶ y
            │
  x3 ●──w3──┘

  Rosenblatt: a neuron
  learns by example