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So don't worry so much about how to use  had had  as a unit of grammar, they will come together naturally when you want to express the verb ' to have ' in the past perfect. Let's consider a different verb for a moment like  to want .
Definition of together - with or in proximity to another person or people, into companionship or close association, at the same time, without interruption; Definition of together - with or in proximity to another person or people, into companionship or close association, at the same time, without interruption; dictionary thesaurus