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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 .
3. When learning English I was told that ordinal numbers should always be used with the before them. But I often see that this is not always so strict, for example I heard the phrase April first instead of April the first.