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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 .
GLHF: Good Luck, Have Fun. While GG is usually said at the end of a match between two or more players, GLHF (Good Luck, Have Fun) can be used as a polite greeting at the beginning of a match.