How to check for duplicate topics before posting a new topic?

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I have tried to find if there are duplicate topics before I post one of my own, but it is only after I post mine that the list of related posts appears - showing a bunch of topics that are very similar if not identical to my own. If I had known that they existed earlier, I might not have posted it in the first place. Is there any way to find out topics related to one that you want to post about? Broad groups are hardly any help, you know. Can you help me?