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Bitcoin is not a stable coin.
To be fair the user didn't say a stable coin, but as a stable currency. Bitcoin is not stable enough to use it for some purposes, but that is to be expected when its value is massively appreciating. One day this may change.
It is not stable. Whatever you want to call it, it is still not a stable currency or coin.
1 Bitcoin is 1 BTC.
Go back to the white of Bitcoin. That's the answer. Now. Don't wait until tomorrow to read it.