I think this is in dispute, we know RH ate there 3-5 times per month. I am not sure we know how often if ever he took Cooper with him.
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I think RH actually ate there close to daily, at the very least, it was very frequent, and one of the interesting insights into Harris is that he always ordered the exact same thing. His friends all said about him that he is a man of rigid habit, down to never deviating from what he ordered at the few restaurants/eateries he frequented.