In this article, I’m going to explain the mental models I use to think about Stacks and why I’m so bullish in the long run. This is the culmination of 4 months studying Stacks, so I hope it proves valuable.
Let’s start with an explanation of the technical aspects, and then we will move on to my thesis on Stacks (Stacks Economy and Future).
If you are not interested in delving into the technical aspects you can skip the sections after "Review" until “Stacks Economy".
Welcome to the Stacks rabbit hole 🕳️
WTF is Stacks? 🧐
Stacks, formerly BlockStack, is a blockchain whose native currency is STX. Specifically, we are in version 2.0 of Stacks, with a completely novel consensus algorithm called Proof of Transfer.
Consensus Algorithms
A consensus algorithm is simply a way to secure the blockchain with a resource. In general, in cryptocurrencies, we find two consensus algorithms: Proof of Work (PoW) and Proof of Stake (PoS).
Bitcoin uses Proof of Work, where the resource used to secure the blockchain is mathematical calculations. These calculations are made with mining rigs, operated by the miners.
Proof of Stake is used in most popular blockchains (including future Ethereum 2.0). In this case, the resource used is the native coins of the blockchain, which are locked for a time. This is known as staking, and the ones that do it, the stakers, fulfill the same function as the PoW miners (securing the blockchain).
Both PoW miners and PoS stakers receive as a reward the new generated coins (inflation) and the fees that users pay for making their transactions.
Each of these two systems has complex trade-offs. In a PoW more energy is spent and many criticize it for not being friendly with the environment. PoS consumes little energy and transactions are processed faster. But it is susceptible to a number of attacks that could even completely paralyze its operation. PoW is often considered superior in security, more resilient and decentralized.
Proof of Transfer (PoX) 😎
Proof of Transfer is similar to PoW in that a resource external to the blockchain is used to secure it and it is similar to PoS in that it does not require specific mining hardware or large amounts of power.
By using an external resource, we speak of a Nakamoto Consensus system (like Bitcoin), with a similar security model.
And what is the resource used to secure Stacks? BTC! Instead of wasting energy or locking coins to mine, we spend BTC. In a way, we are reusing the computational work that was used to mint bitcoins.
Consensus Algorithms like Lotteries 🎟️
A good example to understand consensus algorithms is that of a lottery where each ticket is a unit of the resource that secures the blockchain (computing power, locked coins, etc).
The more tickets (resource units) you have, the higher your chance of winning.
Note: Miners / stakers are in charge of processing transactions and securing the network with a resource.
Their reward for that work consists of newly generated coins and fees from users who transact. This is the "lottery" prize.
With a single lottery ticket it is very unlikely that you will win the prize. In the same way, putting a mining rig to work, it is highly unlikely that you will win the blockchain prize.
That is why in cryptocurrencies, groups called pools are formed, to make the participation in mining / staking profitable.
PoS: Locked coins = lottery tickets 🎟️
PoW: Computing power = lottery tickets 🎟️
PoX: BTC spent = lottery tickets 🎟️
PS: in PoX, for every Bitcoin block mined, there is a Stacks lottery winner. This idea is expanded in the “Stacks Blocks 👿” section.
Stacking of STX 🤑💸
Whereas in PoW, an energy expenditure is incurred. In PoX the expense to mine is in a cryptocurrency.
Stacks miners spend BTC. But how do they spend it? They send it to STX holders, making this asset generate yield in BTC.
STX holders lock their coins and receive the BTC spent by the miners. This is a risk-free return, intrinsic to the Stacks Consensus Algorithm (PoX).
The process of locking STX to receive BTC is called Stacking (different from staking since it has nothing to do with the security of the blockchain and does not involve risks).
Miners secure the blockchain by spending BTC and earn STX. Stackers lock STX and earn the BTC spent by miners. The expenditure to mine is being “recycled".
Review
We have that Stacks is a blockchain and cryptocurrency that is mined by spending BTC and that, if we lock it with stacking, it generates BTC (from miners).
All of this has been an explanation of the most unique technical aspect of Stacks. Let’s continue with other technical aspects that are also very important.
Stacks Blocks 👿
As we know, Stacks miners send BTC transactions to participate in the Stacks mining “lottery”.
Each Bitcoin transaction represents one participant and the amount of BTC sent represents the number of lottery tickets they have.
For each Bitcoin block a lottery is fought where only one Stacks miner will win. That is, of all the miner transactions processed in a Bitcoin block, only one wins.
This means that Stacks churns out blocks at the same rate as Bitcoin (roughly one block every 10 minutes). In other words, Stacks transactions confirm as slowly as Bitcoin... but there is an ace up your sleeve to increase confirmation speed. This ace is the microblocks, which we will talk about later.
Proof of Burn (PoB) 😎🔥👌🏼
In the original design of the consensus algorithm, instead of sending BTC to the stackers, it was destroyed.
Destroying or burning a cryptocurrency consists of sending it to an address that does not belong to anyone and from where it can never be used again.
In this original design, Proof of Burn, Stacks miners competed by destroying BTC. Although Proof of Transfer is used with Stacks 2.0, Proof of Burn is still used at the beginning and end of each cycle (explained below).
Stacking Cycles 🔄
In Proof of Transfer cycles of 2,100 blocks are used (about two weeks). The cycles are made up of the prepare phase (100 blocks) and the reward phase (2,000 blocks).
During the 2,000 blocks of the reward phase, stackers receive BTC.
The transactions carried out by miners consist of:
- Sending BTC to two addresses (or to the burning address when using PoB).
- Register the information of the block of Stacks that they intend to mine.
Therefore, in each cycle, BTC will be sent to a maximum of 4,000 BTC addresses of the stackers (2 addresses per 2,000 blocks). These addresses are known as reward slots.
This does not mean that there can only be 4,000 stackers, but rather that stacking pools must be formed to distribute the BTC based on the amount stacked.
This limitation of 2 reward slots per transaction is made so that Stacks does not overuse Bitcoin’s meager block space (~1.5MB).
When is Proof of Burn used? 🔥🥵🔞
On the other hand, reward slots that are not used will be changed by the BTC burning address (Proof of Burn will be used). There are currently only 136 empty reward slots, meaning that BTC is burned during the final 68 blocks of the cycle. With time and the adoption of stacking all reward slots will be used.
Proof of Burn is also used (and in this case will continue to be) in the prepare phase of the cycle. In this phase Stacks reaches a consensus on which will be the addresses and the reward slots occupied in the new cycle. During these 100 blocks BTC will be burned.
Therefore, Stacks burns ~5% of the BTC and distribute ~95% to stackers.
Microblocks: fast transactions 🚄
In Bitcoin there is a function called "Replace By Fee" or simply RBF, which allows you to replace a transaction with another that pays more fee (before it has been included in a block). Microblocks use this feature to get quick confirmations.
Let’s start with the Stacks mining process. Miners submit their BTC transactions first.
One of all miners will win, but it will only be known when their transactions have been included in a Bitcoin block.
As a Bitcoin block can take several minutes to mine, Stacks transactions often accumulate in the mempool (waiting to be processed by miners).
Then miners can RBF to update their BTC transaction and add Stacks transactions to the block data. Each of these updates is a microblock of Stacks.
Miners are incentivized to add microblocks to earn more fees in case their block is not full. Microblocks improve user experience by displaying quick confirmations. The probability that a transaction on a microblock will be confirmed in Bitcoin is very close to 100% if all miners use this feature (all mining transactions commit to your transaction).
The use of microblocks is recommended for low value transactions as they are considered somewhat less secure than “normal” block transactions.
For example, block 29,720 of Stacks included 5 transactions. But 22 more were added using two microblocks on the fly. The respective winning BTC transaction was updated twice to include data from the two microblocks.
Finally the respective Bitcoin block was mined, and this transaction was the winner (won the "lottery").
Microblocks and Lottery
To be clearer, let’s use the example of the lottery 😎🔥
Imagine that we have a lottery ticket and, as we go along, others appear with a higher prize (but the same probability of winning). The fact is that we can change our ticket for a new one by paying a little more. The rational thing is that we do it since our potential profit increases a lot.
This is exactly what happens in Stacks. Transactions that pay more fee appear and miners can update their "ticket" (change the data about their block of Stacks) to include them.
These ticket updates (microblocks) obviously occur before a lottery winner is chosen (the Bitcoin block is mined). Until this happens, miners' tickets can continue to be updated.
And when a winner is chosen, another new lottery begins (Bitcoin miners start mining the next block and Stacks miners send their new transactions to participate).
Using the immutability of Bitcoin
Unlike the rest of blockchains, the history of the Stacks blockchain, including forks, is publicly recorded forever (on the Bitcoin blockchain).
Note: a fork is when there are two blocks of the same height (as seen in the illustration below).
While in PoW and PoS miners can create blocks in private, in Stacks the process is completely public, since it occurs on the Bitcoin blockchain itself.
Any attempted attack by the miners (51% attack) will be public. And by being discoverable, they can be countered by supporting honest miners.
An attacker is also limited by time, as only one Stacks block can be produced for each Bitcoin block. A 51% attack on Stacks requires not only spending BTC, but also time.
Clarity: Stacks smart contract language 📝
At Stacks, a security-focused language for smart contracts called Clarity has been developed.
Unlike Solidity, the predominant language in Ethereum, Clarity is not Turing-complete. The Stacks blockchain interprets it natively so it doesn’t need a compiler (as with Ethereum). It is also a "decidable" language (we can know how the code will be executed) and it has "postconditions", to avoid situations in which a contract does something that we did not expect.
All these features make it a very secure smart contract language. It should be mentioned that it is also supported by Algorand.
Gaia: Decentralized Storage System
Another of the Lego blocks the Stacks team has been working on is decentralized storage.
This is a common need for decentralized applications as storing information on the blockchain is not feasible. The system they have developed is called Gaia.
Visibility over Bitcoin
And finishing the technical part, a very powerful feature of Stacks is that it has visibility over the Bitcoin blockchain. As mining activity occurs on Bitcoin, Stacks nodes also run Bitcoin nodes to verify this information.
A node is a computer that verifies the information on the blockchain and maintains the global shared state. If you don’t understand it, better search for it on Google.
This is why Stacks can verify Bitcoin information, that is, smart contracts can react to events on Bitcoin.
For example, let’s imagine a trustless BTC loan. Alice lends BTC to Bob, and Bob leaves his collateral in stablecoins on Stacks. If after a date, Alice does not receive the BTC + interest in an address, the smart contract in Stacks can verify it and Alice can take Bob’s collateral.
Another use of this feature is buying assets on Stacks such as NFTs or fungible tokens (citycoins, memecoins, stablecoins, etc.) with BTC.
Stacks Economy 📖
Having seen the key technical aspects of Stacks, let’s move on to the economic part of the article, a little lighter 🙈
Stacks Monetary Policy 📊
- 1,000 STX per block during the first 4 years (210,000 blocks).
- 500 STX per block for the next 4 years.
- 250 STX per block for the next 4 years.
- 125 STX per block in perpetuity.
At the beginning of Stacks, a pre-mine was carried out aimed at different token offers (2017 and 2019), founders, independent entities, etc. In total, this amount is 1,320 million STX (which will be unlocked until 2025).
Currently, there are 1.25 billion STX in circulation. With these data, STX inflation is around 4.5% per year.
After 4 years, inflation will be less than 1.7%. At 4 years, less than 0.82%. And finally less than 0.38%.
All this assuming there is no change in Stacks' monetary policy, something that cannot be ruled out.
Regulatory clarity
The premine is perhaps Stacks' most objectionable point (from an ethical point of view). It is also true that after Ethereum, practically all cryptocurrencies have used this practice to finance development of projects.
In the case of Stacks, they have been one of the projects with the most regulatory transparency (if not the most). In fact, they conducted the first SEC-rated token offering in US history. Also in 2019 they released a 140+ page disclosure document on the risks of investing in STX.
STX was considered a "security" but after the launch of Stacks 2.0 it stopped being so. Considering that current SEC Chairman Gary Gensler has publicly hinted that most cryptocurrencies could be considered "securities," Stacks' regulatory clarity could play positively in the long run.
What does Stacking yield depend on? 💸💸💸
Stacking yield depends on the block reward miners receive and the amount of coins stacked.
If, for a week, miners make $ 1 million (in STX), they will spend almost $ 1 million (in BTC). That million dollars in BTC will be distributed among stackers. Therefore, the fewer stackers there are, the more percentage of the million stackers will take, and vice versa.
The difference between what miners spend and what they earn is their profit. As mining is a competitive activity, this margin tends to decrease. That is why we say that miners spend almost as much of what they earn.
The higher the block reward, the higher the mining spending and the higher the stacking yield.
In turn, the block reward (what the miners earn) is made up of:
- Block subsidy (inflation)
- User fees (gas fees)
As inflation is decreasing (as we explained in the Monetary Policy section), stacking yield will decrease.
But if the utility of Stacks increases (miners receive more money from fees), stacking yield will not decrease that much, will stay the same or will increase (depending on how much is collected by fees).
Next I am going to explain the mental model that I use to think about Stacking and PoX, so stay tuned 😎🚀
The PoX superpower
If we think about it carefully, Stacking is a way to compensate for inflation through payments in BTC. Recall that for every dollar of STX created, the miners transfer (almost) a dollar of BTC to stackers.
With an inflation of 4.5%, if 100% of the STX supply were stacked, the yield would be 4.5%. PoX would simply serve to offset inflation. The net result would be like holding an asset without inflation or deflation.
By receiving 4.5% in BTC, we could swap it to STX, and keep the same percentage of supply. That is, inflation for stackers would be 0%.
But for 100% of the STX supply to be stacked is unrealistic. In practice, the percentage is usually less than 50%. For this reason, Stacking yield is usually around 10% (more than two times higher than inflation).
A deflationary currency is one with a supply that is not only limited, but decreasing over time.
The same effect can be achieved if our quantity of that currency increases.
For example, having 1 coin out of a total of 100, I have 1%. If the total is cut in half, I will have 2% (1 coin in 50). But if instead, I win another coin, I will have also multiplied my percentage by 2 (2 coins out of 100).
Stackers will always receive compensation in BTC greater than inflation (because less than 100% of the supply is stacked). And if they converted the BTC to STX, their percentage of the total supply would be increasing. You could say that STX is deflationary for stackers.
Regardless of the inflation that exists in Stacks, stackers will be overcompensated. Inflation shouldn’t be a problem because stacking is widely accessible and risk-free. Long-term holders should opt-in for it.
But the most interesting thing is the second part of the equation: the fees that miners earn. If the use and utility of Stacks increased, miners would collect more fees and BTC spending would increase.
If we add to this scalability solutions that collect fees for miners such as subnets, appchains and rollups, the block reward could increase a lot, causing a large increase in the Stacking yield.
In this case, the yield would not only come from inflation, but also from the usefulness of the platform. The value generated by Stacks would be being absorbed by the stackers via BTC payouts.
The higher the utility of Stacks -> the higher the yield it can generate -> the greater incentive to hold and stack STX -> higher price
Similarity of PoX to EIP-1559
In a recent Ethereum update a proposal called EIP-1559 was added. What was modified with this was the fee market in Ethereum, causing a part of the fees to be burned.
This change fixes some mismatches, but also allows ETH to absorb value generated on the platform.
ETH burning makes the circulating ETH increase in value. There is even the possibility that more will be destroyed than is issued, making ETH a deflationary asset.
In Stacks, unlike Ethereum, the value generated in fees is not absorbed by holders destroying STX, but with BTC payouts, which is a much more explicit way.
In addition, stackers receive almost 100% of the value of the block reward (fees and inflation), instead of only a part of the fees (basefee).
For the latter, in terms of value absorption, Stacks is superior to Ethereum. In addition, this value is not distributed to all STX holders, but to those who lock it (reducing the liquid supply).
And unlike Ethereum, we are certain that STX is always “deflationary" for stackers (the amount stacked is less than 100% of the supply).
In the same way, we also have the certainty that Bitcoin is deflationary because Stacks burns BTC with Proof of Burn. As the amount of BTC produced tends to 0, there will come a point where the supply starts to decrease. Currently more than 248 bitcoins have been burned.
- By owning BTC, your percentage of the supply increases in the long run.
- By owning STX and stacking, your percentage of the BTC supply increases. This value can be changed to STX, so that your percentage of the STX supply increases.
Note: At Friedger Pool, Stacking rewards are not received in BTC, but directly in STX.
Stacking Compound Interest
If you have 1,000 STX stacked (currently 10% per year), you will earn 100 STX per year (if you change the BTC to STX). The following year you will have 1,100 STX, with which you will generate 110 STX. And so on.
If we add to this that the price of STX can increase, we are talking about a double compound interest. Earning more STX, which in turn is worth more.
There can even be triple compound interest if we use the stacked STX to provide liquidity for some protocols like Arkadiko (e.g. minting a collaterized stablecoin with our STX and lending it).
Using PoX to fund communities 📈📈📈
Proof of Transfer has proven to be effective for raising money with mining (on Stacks aimed at stackers).
Until now only Stacks implemented PoX, but the same mining mechanism can be implemented in other fungible tokens on a blockchain (PoX-lite).
This is the case with CityCoins, assets that aim to help cities raise money privately (without taxes). More than currencies, we must consider them a kind of crypto-share on cities.
Instead of being mined by spending BTC, CityCoins are mined by spending STX. 30% goes to the government of the city, and 70% to the stackers of the asset.
Launch begins with mining, that is, there is no premine. This possibility does not exist in a PoS system because without coins in circulation, staking cannot be done. PoX and PoX-lite allow for fair cryptoassets launches.
This experiment has already been tested in Miami, launching MiamiCoin (MIA). And to the surprise of many (included me), it has been successful. With MIA mining, Miami government has so far raised more than 6 million STX, valued at more than $ 9 million.
Given this, Miami voted unanimously to accept the funds, which for now will be used to make housing in Miami more accessible. But in the future it is likely that Miami will retain STX in its treasury and generate BTC with it.
Some uses of MIA are stacking to earn STX, its interchangeability for STX, BTC or any asset on the Stacks blockchain, its use as collateral to request loans, voting with coins (as if it were a Miami DAO) and Proof of Hodl.
This last concept consists of establishing physical locations (either in Miami or internationally) whose access is restricted to MIA holders.
"Show me the incentive, I’ll show you the result." - Charlie Munger
If the Miamicoin experiment is successful, it is inevitable that other cities are set in this model to be financed. All these "Start-Up cities" will have the possibility to maintain STX and BTC in its treasury. And Stacks utility will increase (can be used to mine and trade these assets).
Apps on Stacks
The applications that stand out the most are:
- Boom: App to create and market NFTs. There are also NFTs that generate yield in STX or BTC. These are boomboxes, which are created by stacking STX. Owning a boombox offers you the yield associated with stacking. It can be said that they are NFTs with intrinsic value.
- ALEX: A DeFi protocol, with various financial derivatives such as DEXes, BTC, STX and USDC loans and Yield Farming.
- Arkadiko: A loan / borrowing protocol for different assets, including a decentralized stablecoin, USDA. The collateral can be deposited in STX, being able to pay the interests with stacking. It also has a DEX integrated.
- Satoshibles: A collection of Satoshi Nakamoto-themed NFTs. They are in Ethereum but the team is building a bridge so that they can be transferred to Stacks, on Bitcoin.
- Moonray: A RPG action videogame that will use NFTS and a tokenomic system on stacks. This is probably the most professional game throughout crypto industry.
Some items such as weapons and shields will be NFTs with different qualities, and you will have the possibility of winning BTC by playing.
These are just some of the companies and projects that are being built on Stacks. More than 25 companies are being trained by the Stacks Accelerator and advised by some entrepreneurs and industry leaders.
Stacks is good for Bitcoin 😎👌🏼
Note: The security budget of a blockchain is the amount of money that miners receive. That is, the block reward. The larger it is, the more resources miners will use to secure the blockchain.
- Stacks increases the demand and utility of BTC for use in mining.
- Stacks destroys BTC, making it deflationary in the long run.
- Stacks increases BTC’s security budget. It does this by paying high fees to BTC miners (doing Replace By Fee).
- Stacks increases the utility of BTC, for example by allowing trustless loans or swaps.
- Stacks shares infrastructure with BTC so it also invests in BTC development.
This is why the relationship between Stacks and Bitcoin is not parasitic (as some bitcoiners have suggested), but symbiotic. The Stacks and Bitcoin duo is a win-win.
The future of sidechains
Trustless sidechains may become a reality for Bitcoin in a few years. Perhaps the most feasible way is using Zero Knowledge proofs like ZK-Snarks (like Zendoo sidechains).
Sidechains are blockchains where the native coin belongs to another blockchain (the main one). This would allow moving BTC from Bitcoin to blockchains similar to Ethereum, Monero, Bitcoin Cash, etc. and vice versa.
Sidechains would definitely open the doors to an innovation on Bitcoin never seen before. The usefulness of Bitcoin would greatly increase as it could be used on any kind of blockchain.
In this future it is very possible that Stacks ended up as a Bitcoin sidechain. The native coins of Stacks would be Stacks-BTC (which could be used in any smart contract) and STX, whose main role would be stacking.
The two current Bitcoin sidechains (require trust) are RSK and Liquid, the former using a PoW consensus algorithm (with Merge Mining) and the latter being a federated system (more centralized).
Merge Mining allows miners to reuse their computational power to mine other blockchains (in this case sidechains) as well. At RSK a subset of Bitcoin miners use it to earn higher reward for the same work. This potentially increases Bitcoin’s security budget in the long run.
In addition to PoW with Merge Mining, future sidechains could be PoS. In this case, BTC miners do not benefit and, therefore, the Bitcoin security budget does not increase.
Alternatively, another consensus protocol of a sidechain could be PoX. And more specifically Stacks, a blockchain that has already been successfully bootstrapped, with some security and network effects.
Stacks-BTC would benefit from a minimal security budget coming from the STX block subsidy (STX inflation). To this should be added the fees that Stacks would already be generating.
By using Stacks-BTC, you would be contributing to Bitcoin through the points mentioned previously.
Thanks to STX the potential BTC deflation is greater since block subsidy adds value to the block reward. And the higher the block reward, the higher the BTC spent by miners (~5% burned).
STX is a Stacks share
Perhaps the best way to see STX is as a platform share. As we have explained, thanks to PoX, stackers receive the value generated by fees (+ an inflation compensation). This is the same as saying that STX offers the right to collect the value generated by Stacks.
For example, if I have 1% of the supply of Stacks, I can collect 1% of fees paid. Although I will actually charge more. If 50% of the supply is stacked, I will charge 2%.
“Shareholders” can use BTC payouts to finance projects and developers - you don’t even need to sell STX - or for any expenses.
Something similar happens in PoS, although stakers do incur risks by actively participating in the consensus protocol. Also in stacking, payments are received in BTC, the most liquid cryptocurrency. They could even be received through the Lightning Network (with submarine swaps).
Lightning Network is a scalability technology that enables thousands of BTC transactions per second and micropayments.
A submarine swap consists of sending BTC from the blockchain to Lightning privately.
The future of Stacks🚀
For everything explained in this article, Stacks is one of the most interesting projects with the most potential in the ecosystem.
Its consensus protocol makes STX a risk-free productive asset, it is a blockchain that uses Bitcoin in a novel way, adds new use cases and strengthens it as digital gold and provides developers with a powerful and secure smart contract language.
We can also see experimentation with PoX that has led to other applications such as CityCoins (private financing of cities), AppChains (other blockchains such as Stacks on Stacks) and Boomboxes (NFTs that generate BTC yield).
The role that Stacks can play in bringing some smart contract use cases to Bitcoin can add a ton of value for both Bitcoin and Stacks.
For example, a whole culture of Bitcoin NFTs could emerge on Stacks (NFTs purchased with BTC). Watching what’s happening in other ecosystems and knowing how big Bitcoin community is, we should definitely not underestimate the size of this market.
NFTs originated with Bitcoin (Rare Pepes), and will return to Bitcoin.
As the use of the network increases, and to maintain the layer 1 (main blockchain of Stacks) decentralized, subnets and other layers 2 will be key. Specifically subnets will be production-ready entering 2022.
This increase in use will be reflected in the Stacking yield and price of STX. But the philosophy of the community is clear: do not hype, write code in the shadows and long term thinking. That is precisely why you may know Cardano, but not Stacks.
All this information has not widely reached the market, so the price of STX is probably very undervalued. Stacks' market cap is less than $ 2 billion, compared to Solana’s 50 billion, Cardano’s 70 billion, or Ethereum’s 400 billion.
If Stack reached the same market cap that Solana has today, we would be talking about an increase of 30x, with a price of $ 40. And this would not be an especially optimistic scenario.
Most importantly, Stacks is a new world on top of Bitcoin, the most durable layer of the Internet. Hype is not needed to build the future of web 3.0 around Bitcoin, and organic growth wins in the long run.
Give the shadowy super-coders some more years and you will not believe what they will have built on top.
Thanks for reading 🙏🏼 ₿ ♡ Ӿ
