But the regression theorem requires that the money have value each prior day, even when you get all the way back to the day before the moneystuff became money. Hence the need for an intrinsic value. According to the regression theorem, the pizza maker must have some idea of bitcoin worth, and with no prior exchanges it must have been the intrinsic value. Thats why it seems the regression theorem does not work for bitcoins. You either have to use fantasy and invent some intrinsic value, or you have to modernize the regression theorem.
"People today expect money to have a certain purchasing power tomorrow, because of their memory of its purchasing power yesterday."
There is no intrinsic value about money. There is no intrinsic value about any and all goods and services in Austrian Economics.
It is "expected purchasing power" depending on the "past purchasing power".
The reason the exchange happened is immaterial after it happened.
It doesn't matter What matter is
the exchange happened.
The pizza maker could have accepted the transaction for a lot of reasons or just wrote "Yes" in the wrong chat.
The effect is the day after the seller of bitcoin will remember he sold 10K bitcoins for 2 pizzas (10 US$ retail price, 5 US$ cost) (so he valued the 10K bitcoins he sold less than two pizzas) and the pizza seller would remember he bough 10k bitcoins for two pizzas, so he valued them more than the two pizzas he sold. And others would remember the same.
In the mean time, two pizzas would be consumed and 10K bitcoins would be added on the balance sheet of the pizza maker and subtracted from the balance sheet of the coin seller.
Now people know pizzas was bough for bitcoins in the past and they know a price point.
If enough of these exchanges happened in a short time then market take care of the rest.
Because bitcoin behave as a currency better than other types of currency (because it was designed to do so) as it start to be used (for whatever reason even just random accident) it become a preferred currency to hold than the other currencies. So people tend to exchange their paper currencies for bitcoin and spend their paper currencies more than bitcoin. This raise the price of bitcoin in the other paper currencies and reinforce the feedback.