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https://en.wikipedia.org/wiki/Frisch%E2%80%93Waugh%E2%80%93Lovell_theorem https://taweihuang.hpd.io/2020/03/23/double-machine-learning/ https://medium.com/@med.hmamouch99/double-machine-learning-for-causal-inference-a-practical-guide-5d85b77aa586