Subject: Re: [bitcoin-dev] Surprisingly, Tail Emission Is Not Inflationary

From: Eric Voskuil <[email-masked]>
Date: Sat, 9 Jul 2022 07:26:22 -0700

> Due to lost coins, a tail emission/fixed reward actually results in a stable money supply. Not an (monetarily) inflationary supply.

This observation is not a proof of lost coins, that is an assumption. It is the provable consequence of market, as opposed to monopoly, production.

https://github.com/libbitcoin/libbitcoin-system/wiki/Inflation-Principle

Mises’ unfortunate error in the application of the Cantillon Effect to gold perpetuates this misperception. One could imagine applying this theory to all goods, not just money, and conclude perpetual loss of value in everything produced, as a consequence of production. One might then be tempted to attribute the fact that this is not observable to loss/depreciation/consumption. While it is certainly possible that the amount of gold produced every year is offset by the amount lost, this of course implies that all of it is lost.

“Circulation” does not determine demand, all money is always held by someone. Changing hands only changes who owns the money, not its purchasing power. See Rothbard’s critique of monetary “velocity”.

e

> On Jul 9, 2022, at 05:47, Peter Todd via bitcoin-dev <[email-masked]> wrote:
> 
> New blog post:
> 
> https://petertodd.org/2022/surprisingly-tail-emission-is-not-inflationary
> 
> tl;dr: Due to lost coins, a tail emission/fixed reward actually results in a
> stable money supply. Not an (monetarily) inflationary supply.
> 
> ...and for the purposes of reply/discussion, attached is the article itself in
> markdown format:
> 
> ---
> layout: post
> title:  "Surprisingly, Tail Emission Is Not Inflationary"
> date:   2022-07-09
> tags:
> - bitcoin
> - monero
> ---
> 
> At present, all notable proof-of-work currencies reward miners with both a block
> reward, and transaction fees. With most currencies (including Bitcoin) phasing
> out block rewards over time. However in no currency have transaction fees
> consistently been more than 5% to 10% of the total mining
> reward[^fee-in-reward], with the exception of Ethereum, from June 2020 to Aug 2021.
> To date no proof-of-work currency has ever operated solely on transaction
> fees[^pow-tweet], and academic analysis has found that in this condition block
> generation is unstable.[^instability-without-block-reward] To paraphrase Andrew
> Poelstra, it's a scary phase change that no other coin has gone through.[^apoelstra-quote]
> 
> [^pow-tweet]: [I asked on Twitter](https://twitter.com/peterktodd/status/1543231264597090304) and no-one replied with counter-examples.
> 
> [^fee-in-reward]: [Average Fee Percentage in Total Block Reward](https://bitinfocharts.com/comparison/fee_to_reward-btc-eth-bch-ltc-doge-xmr-bsv-dash-zec.html#alltime)
> 
> [^instability-without-block-reward]: [On the Instability of Bitcoin Without the Block Reward](https://www.cs.princeton.edu/~arvindn/publications/mining_CCS.pdf)
> 
> [^apoelstra-quote]: [From a panel at TABConf 2021](https://twitter.com/peterktodd/status/1457066946898317316)
> 
> Monero has chosen to implement what they call [tail
> emission](https://www.getmonero.org/resources/moneropedia/tail-emission.html):
> a fixed reward per block that continues indefinitely. Dogecoin also has a fixed
> reward, which they widely - and incorrectly - refer to as an "abundant" supply[^dogecoin-abundant].
> 
> [^dogecoin-abundant]: Googling "dogecoin abundant" returns dozens of hits.
> 
> This article will show that a fixed block reward does **not** lead to an
> abundant supply. In fact, due to the inevitability of lost coins, a fixed
> reward converges to a **stable** monetary supply that is neither inflationary
> nor deflationary, with the total supply proportional to rate of tail emission
> and probability of coin loss.
> 
> Credit where credit is due: after writing the bulk of this article I found out
> that Monero developer [smooth_xmr](https://www.reddit.com/user/smooth_xmr/)
> also observed that tail emission results in a stable coin supply
> [a few years ago](https://www.reddit.com/r/Monero/comments/4z0azk/maam_28_monero_ask_anything_monday/d6sixyi/).
> There's probably others too: it's a pretty obvious result.
> 
> 
> <div markdown="1" class="post-toc">
> # Contents
> {:.no_toc}
> 0. TOC
> {:toc}
> </div>
> 
> ## Modeling the Fixed-Reward Monetary Supply
> 
> Since the number of blocks is large, we can model the monetary supply as a
> continuous function $$N(t)$$, where $$t$$ is a given moment in time. If the
> block reward is fixed we can model the reward as a slope $$k$$ added to an
> initial supply $$N_0$$:
> 
> $$
> N(t) = N_0 + kt
> $$
> 
> Of course, this isn't realistic as coins are constantly being lost due to
> deaths, forgotten passphrases, boating accidents, etc. These losses are
> independent: I'm not any more or less likely to forget my passphrase because
> you recently lost your coins in a boating accident — an accident I probably
> don't even know happened. Since the number of individual coins (and their
> owners) is large — as with the number of blocks — we can model this loss as
> though it happens continuously.
> 
> Since coins can only be lost once, the *rate* of coin loss at time $$t$$ is
> proportional to the total supply *at that moment* in time. So let's look at the
> *first derivative* of our fixed-reward coin supply:
> 
> $$
> \frac{dN(t)}{dt} = k
> $$
> 
> ...and subtract from it the lost coins, using $$\lambda$$ as our [coin loss
> constant](https://en.wikipedia.org/wiki/Exponential_decay):
> 
> $$
> \frac{dN(t)}{dt} = k - \lambda N(t)
> $$
> 
> That's a first-order differential equation, which can be easily solved with
> separation of variables to get:
> 
> $$
> N(t) = \frac{k}{\lambda} - Ce^{-\lambda t}
> $$
> 
> To remove the integration constant $$C$$, let's look at $$t = 0$$, where the
> coin supply is $$N_0$$:
> 
> $$
> \begin{align}
>    N_0 &= \frac{k}{\lambda} - Ce^{-\lambda 0} = \frac{k}{\lambda} - C \\
>      C &= \frac{k}{\lambda} - N_0
> \end{align}
> $$
> 
> Thus:
> 
> $$
> \begin{align}
>    N(t) &= \frac{k}{\lambda} - \left(\frac{k}{\lambda} - N_0 \right)e^{-\lambda t} \\
>         &= \frac{k}{\lambda} + \left(N_0 - \frac{k}{\lambda} \right)e^{-\lambda t}
> \end{align}
> $$
> 
> 
> ## Long Term Coin Supply
> 
> It's easy to see that in the long run, the second half of the coin supply
> equation goes to zero because $$\lim_{t \to \infty} e^{-\lambda t} = 0$$:
> 
> $$
> \begin{align}
>    \lim_{t \to \infty} N(t) &= \lim_{t \to \infty} \left[ \frac{k}{\lambda} + \left(N_0 - \frac{k}{\lambda} \right)e^{-\lambda t} \right ] = \frac{k}{\lambda} \\
>                   N(\infty) &= \frac{k}{\lambda}
> \end{align}
> $$
> 
> An intuitive explanation for this result is that in the long run, the initial
> supply $$N_0$$ doesn't matter, because approximately all of those coins will
> eventually be lost. Thus in the long run, the coin supply will converge towards
> $$\frac{k}{\lambda}$$, the point where coins are created just as fast as they
> are lost.
> 
> 
> ## Short Term Dynamics and Economic Considerations
> 
> Of course, the intuitive explanation for why supply converges to
> $$\frac{k}{\lambda}$$, also tells us that supply must converge fairly slowly:
> if 1% of something is lost per year, after 100 years 37% of the initial supply
> remains. It's not clear what the rate of lost coins actually is in a mature,
> valuable, coin. But 1%/year is likely to be a good guess — quite possibly less.
> 
> In the case of Monero, they've introduced tail emission at a point where it
> represents a 0.9% apparent monetary inflation rate[^p2pool-tail]. Since the number of
> previously lost coins, and the current rate of coin loss, is
> unknown[^unknowable] it's not possible to know exactly what the true monetary
> inflation rate is right now. But regardless, the rate will only converge
> towards zero going forward.
> 
> [^unknowable]: Being a privacy coin with [shielded amounts](https://localmonero.co/blocks/richlist), it's not even possible to get an estimate of the total amount of XMR in active circulation.
> 
> [^p2pool-tail]: P2Pool operates [a page with real-time date figures](https://p2pool.io/tail.html).
> 
> If an existing coin decides to implement tail emission as a means to fund
> security, choosing an appropriate emission rate is simple: decide on the
> maximum amount of inflation you are willing to have in the worst case, and set
> the tail emission accordingly. In reality monetary inflation will be even lower
> on day zero due to lost coins, and in the long run, it will converge towards
> zero.
> 
> The fact is, economic volatility dwarfs the effect of small amounts of
> inflation. Even a 0.5% inflation rate over 50 years only leads to a 22% drop.
> Meanwhile at the time of writing, Bitcoin has dropped 36% in the past year, and
> gained 993% over the past 5 years. While this discussion is a nice excuse to
> use some mildly interesting math, in the end it's totally pedantic.
> 
> ## Could Bitcoin Add Tail Emission?
> 
> ...and why could Monero?
> 
> Adding tail emission to Bitcoin would be a hard fork: a incompatible rule
> change that existing Bitcoin nodes would reject as invalid. While Monero was
> able to get sufficiently broad consensus in the community to implement tail
> emission, it's unclear at best if it would ever be possible to achieve that for
> the much larger[^btc-vs-xmr-market-cap] Bitcoin. Additionally, Monero has a
> culture of frequent hard forks that simply does not exist in Bitcoin.
> 
> [^btc-vs-xmr-market-cap]: [As of writing](https://web.archive.org/web/20220708143920/https://www.coingecko.com/), the apparent market cap of Bitcoin is $409 billion, almost 200x larger than Monero's $2.3 billion.
> 
> Ultimately, as long as a substantial fraction of the Bitcoin community continue
> to run full nodes, the only way tail emission could ever be added to Bitcoin is
> by convincing that same community that it is a good idea.
> 
> 
> ## Footnotes
> _______________________________________________
> bitcoin-dev mailing list
> [email-masked]
> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev