Automatic shape inference lets layers determine their input shape from the first tensor they receive, so connected layers can create compatible weights without explicit input-size arguments. section 3.6.2
A dense layer infers its input size
Create a 32-unit dense layer, pass it a tensor shaped (2, 784), and receive an output shaped (2, 32). The layer uses the inferred input dimension, 784, to create its weight matrix. section 3.6.2
