Thank you cocqui 33, I have added that link to my Evernote for permanent reference.

OK, so I have a follow on question: when bitcoin gets lost like that, or when it gets seized by a government, as recently happened in the news, like this: https://blockchain.info/address/1F1tAaz5x1HUXrCNLbtMDqcw6o5GNn4xqX, what happens to it in the long run? Is it forever out of circulation?