Google Colaboratory - MNIST https://colab.research.google.com/drive/15G_LiYUGbhXzUv5x0EHAzuH8twn7JBN5
Keras https://keras.io/ https://keras.io/api/models/sequential/ https://keras.io/guides/sequential_model/ https://keras.io/ja/getting-started/sequential-model-guide/