You keep talking about gold coins on the one hand and the US Dollar on the other hand. Sorry if you are loosing me here.
Which dictionary defines Gold Coin as Dollar, in which lemma, and how can it predict and continuisly update the exchange rate if there is no authority to poll?
The United States Constitution does the following:
* It permits the Federal government to coin money and regulate its value.
* It specifically forbids states from making anything other than gold and silver coins legal tender. (This part is why Arizona can't declare Bitcoin as legal tender.)
Money and legal tender are related, but not the same concept.
The Legal Tender Act of 1862 (an act of the Federal government) added paper notes as legal tender. Constitutionally, states could not do this, but the Feds can. Due to the Supremacy Clause (https://en.wikipedia.org/wiki/Supremacy_Clause) this law cannot be overridden by the states; they cannot pass a law making paper notes not legal tender.
Gold coins are still legal tender. However, their value as metal is now massively more than their value as tender, so no one uses them as such. For example, a $20 gold coin sold in 2002 for $7,590,020; metal-wise it's worth about $2k, and currency-wise it's worth what it says on the coin, $20. You could use that coin to pay a $20 debt, but it would be a bad decision.
(You could come to an agreement with your creditor to accept it for any value to satisfy the debt, but your creditor is not required to do so.)
Which dictionary defines Gold Coin as Dollar, in which lemma, and how can it predict and continuisly update the exchange rate if there is no authority to poll?