What is a "crypto-currency"? What are Bitcoins and all the rest of the crypto-currency pack?

They are digits on computers, and nothing more. What is "a digit on a computer"? The definition would seem to run along the lines of "an electric charge in a computer memory".

If the ownership of a crypto-currency digit on a computer, or more exactly, on  a "blockchain system" of computers, constituted a legal right to a thing that has objective existence, say 1 kilo of copper, or 1 ounce of silver, or 1 ounce of gold, or any other physically existing commodity in a legally constituted depository, then I would have no problem with such a "crypto-currency". However, so far as I know,  none of the crypto-currencies carry with them any legal right to the ownership of anything tangible at all. ...

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