Introduction and summary
Cryptocurrency markets have recently been plagued with uncertainty, leading a majority of Americans who have heard of these digital assets to lack confidence in their safety and reliability.1 Sadly, many people have invested and lost much of their life savings after being lured into the exaggerated promises of cryptocurrency.2 This has only worsened inequities in the financial markets and wealth accumulation3 and led to scams,4 alleged Ponzi schemes,5 and charges of alleged money laundering6—activities that seem to be the primary attraction of these markets.
Still, millions of people continue to own digital assets.7 And crypto advocates continue to claim that cryptocurrency is somehow innovative and special and therefore should not be taxed or treated like other assets and transactions.8 Hiding behind unproven claims that cryptocurrency is the answer to wealth accumulation for low-income people,9 they continue to push policymakers to apply looser standards to cryptocurrency than those that apply to other financial assets.10
Current tax rules apply to cryptocurrency transactions in exactly the same way they apply to transactions involving any other type of asset.
While the future of cryptocurrencies is uncertain, the application of tax laws to cryptocurrency transactions generally is not. With relatively few exceptions, current tax rules apply to cryptocurrency transactions in exactly the same way they apply to transactions involving any other type of asset.11 One simple premise applies: All income is taxable, including income from cryptocurrency transactions.
The U.S. Treasury Department and the IRS should continue to educate taxpayers about how tax laws apply to cryptocurrency transactions and issue guidance in the few areas where there may be uncertainty. Meanwhile, Congress should allow the Treasury and the IRS to act quickly in this regard and avoid confusing consumers with legislation unless there is broad-based agreement on the need for it.
Lax reporting standards for cryptocurrency transactions have fueled the tax gap
The anonymity that makes digital assets attractive to many investors also raises the potential for tax evasion.12 Failure to report information about cryptocurrency transactions contributes to the tax gap—the difference between the amount of tax that taxpayers legally owe and what they actually pay. In its most recent projections, the IRS estimated that the tax gap for tax year 2021 was $688 billion, an increase of more than $138 billion from the prior estimate for tax years 2017–2019.13 The report stated, however, that the IRS cannot fully represent noncompliance in certain areas, including with respect to noncompliance associated with digital assets.14
The amount of legally owed, but unpaid, taxes is significant. As Yale Law School professor and former Treasury Department official Natasha Sarin noted in recent testimony before the Senate Budget Committee: “One year’s worth of uncollected taxes would pay for nearly all of the non-defense discretionary spending that the federal government does. One year’s worth of uncollected taxes would shrink our annual budget deficits by between one-third to one-half.”15 While the magnitude of the gap associated with digital assets is unknown, one estimate by Barclays PLC suggests that at least half of the taxes owed on cryptocurrency transactions go unpaid, costing at least $50 billion per year in lost tax revenues.16 For this reason, the Treasury Department’s most recent Strategic Operating Plan includes an initiative to “enhance detection of noncompliance and increase enforcement activities” for digital assets and other complex, high-risk, and novel emerging issues.17
One estimate by Barclays PLC suggests that at least half of the taxes owed on cryptocurrency transactions go unpaid, costing at least $50 billion per year in lost tax revenues.
The United States must ensure that the use of cryptocurrencies does not undermine the tax system and the critical revenues it generates. There are two approaches that Congress and the IRS can take to accomplish that goal:
- Fix actual problems: Whenever the tax laws are applied to new types of assets or transactions, questions will arise about the nuances of applying the laws, and sometimes loopholes are revealed. In most cases, the IRS has sufficient authority to resolve these issues, and in others, Congress may need to take action. This report identifies issues where immediate action is warranted.
- Avoid making matters worse: Members of Congress should avoid the temptation to appear crypto-savvy and reject lobbyists’ requests to provide special treatment or legislative exceptions when taxing cryptocurrency assets. A handful of such proposals are discussed below. Meanwhile, the IRS should ensure stronger enforcement of existing tax laws. As discussed in this report, the IRS has taken steps to educate taxpayers in the past, but stronger enforcement and better taxpayer education are essential to ensure that the application of existing tax laws to digital assets and transactions runs smoothly.
Congress and the IRS should close cryptocurrency tax loopholes and fix problems that actually exist
All U.S. citizens, residents, and businesses, as well as foreign individuals and businesses that transact business or invest in the United States, are subject to the federal tax laws, and there are no exceptions for transactions involving cryptocurrencies.18
In 2014, the IRS sought to highlight this point in guidance.19 The agency stated that cryptocurrency assets generally are treated as property.20 Thus, a taxpayer who sells or otherwise disposes of cryptocurrency assets may have a gain for tax purposes, depending upon their basis in the property. Any gain would be taxed at ordinary or long-term capital rates, depending on whether the taxpayer held the digital asset as an investment and on the length of time they held the cryptocurrency assets. Some taxpayers may not be aware that this also means that making purchases with cryptocurrency that has appreciated in value since they acquired it may give rise to a taxable gain. As with any other noncash property used to purchase goods or services, the purchase using cryptocurrency is treated for tax purposes as if the person sold the asset—in this case, the cryptocurrency—and used the proceeds to make the subsequent purchase.
Learn more about crypto assets
When a person receives cryptocurrency in exchange for performing services, the basic tax rules also apply: If they are paid by an employer, the value of the cryptocurrency is subject to federal income tax withholding, Federal Insurance Contributions Act (FICA) tax, and the Federal Unemployment Tax Act (FUTA) tax, and it is reported as income on a Form W-2, the Wage and Tax Statement.21 Payments to independent contractors made in cryptocurrency are subject to self-employment taxes (SECA), and depending on the amount of the payment, reporting may be required on a Form 1099.22 Thus, when a successful miner of virtual currencies receives cryptocurrency in return for their services, the fair market value of the virtual currency on the date it is received is income for tax purposes and subject to income and, potentially, self-employment taxes.
[There are] a handful of circumstances in which the application of existing tax laws to cryptocurrency transactions is unclear. The IRS has the authority to clarify most of these circumstances and should take … steps … to both protect federal revenues and dispel inaccurate claims made by cryptocurrency advocates.
Similarly, businesses that accept cryptocurrency assets as payment must include the value of the assets in income for tax purposes. And companies that invest in cryptocurrency assets for profit must treat those investments the same as any similar company investment for tax purposes.
Yet more recently, policymakers and tax experts have identified a handful of circumstances in which the application of existing tax laws to cryptocurrency transactions is unclear. The IRS has the authority to clarify most of these circumstances and should take the following steps as soon as possible to both protect federal revenues and dispel inaccurate claims made by cryptocurrency advocates.
Clarify broker and other information reporting
The U.S. tax system relies on individuals and businesses to voluntarily report their income and other information necessary to determine their tax liability. Because of the potential for tax avoidance and tax evasion, the tax code requires certain third parties to report information needed to verify tax liability. For example, under Internal Revenue Code (IRC) Section 6045, brokers must report information on gains or losses from transactions to their clients, who then can report their income correctly, and to the IRS.23 The IRS cross-checks the amount on the tax return with the information it received from the taxpayer’s broker. Notably, tax return items that are subject to at least some third-party information reporting have an 85 percent compliance rate.24
The Treasury and IRS have long had the authority to determine whether digital asset brokers are required to report pursuant to Section 6045. However, cryptocurrency brokers have leaned on the anonymity of transactions on the blockchain—the underlying technology on which cryptocurrency assets are based—to claim that they are not required to comply with tax code reporting requirements that are applicable to other brokers. As the number of transactions these brokers manage increases, this could enable an ever-increasing volume of transactions in which customer gains go unreported and thus untaxed, with a corresponding loss of revenues to the Treasury.
To avoid this outcome, the Infrastructure Investment and Jobs Act (IIJA) of 2021 clarified that brokers of digital asset transactions should be treated like other brokers who get paid to effectuate transfers of property or services.25 It also clarified that digital assets, defined broadly, constitute “covered securities” for purposes of this disclosure.26 Section 6045 of the tax code requires brokers to furnish the IRS with identifying information about their customers, including gross proceeds of the transactions.27 In addition, brokers are required under IRC Section 6050I to report to the IRS any transactions made with cash or digital currency of more than $10,00028—a provision aimed at detecting money laundering, terrorism financing, and other nefarious activities. After a long delay, the Treasury Department released proposed rules governing the new broker reporting requirements in late August 2023.29 Unfortunately, however, the proposed rules delay implementation of the new broker reporting requirements until 2026, a move that will result in a substantial loss of revenue in both 2023 and 2024, likely in the range of several billion dollars.30
In addition to clarifying the definition of “broker,” as Congress did in the IIJA, other steps are needed to ensure that individuals and entities engaged in cryptocurrency transactions report information that is essential to determining tax liability. For example, in follow-up guidance on the IIJA provision, the IRS should require domestic exchanges and wallet providers to report to the IRS the number of coins and tokens that become available to customers or wallets they manage after a contentious “hard fork” or “airdrop” giveaway—two actions described in more detail below that can result in income to recipients.
In another important example, the Biden administration’s fiscal year 2024 budget asks Congress to expressly require brokers, such as U.S. digital asset exchanges, to report gross proceeds and other information relating to sales of digital assets by its foreign account holders and, where the customer is a passive entity, provide information about the entity’s substantial foreign owners.31 This proposal is a straightforward clarification that under the provisions of the Foreign Account Tax Compliance Act (FATCA),32 an anti-tax evasion and anti-money laundering statute, the United States in turn can provide information on foreign owners of U.S. accounts to foreign governments that provide reciprocal information about U.S. investors using exchanges based in their countries. This reciprocal exchange of information on U.S. taxpayers that directly or through passive entities engage in digital asset transactions outside the country would help the United States combat the rapidly growing problem of tax evasion, whereby U.S. taxpayers transact with offshore digital asset exchanges and wallet providers without leaving the United States, enabling them to conceal assets and taxable income.
The Biden administration has also proposed to expand current tax law requiring individuals to report any interest they hold in a foreign financial account or certain foreign assets on their tax return.33 This proposal would require tax return information disclosure on any account that holds digital assets maintained by a foreign digital asset exchange or other foreign digital asset service provider.34
Close the wash sale loophole
Lawmakers have considered language that would explicitly clarify that digital asset transactions fall under an existing law that prevents taxpayers from generating tax-deductible losses from the sale and repurchase of securities within a short period of time. Known as a “wash sale,” the taxpayer sells securities at a loss and purchases substantially similar ones within the same time period, then uses the tax-deductible loss to reduce taxable capital gain income on other assets.35 The wash sale rule prohibits deduction of losses attributable to shares of stock or other securities if, within 30 days before or after the transaction that generated the loss, the taxpayer purchases or enters into a contract to purchase substantially identical assets. The taxpayer instead must wait until they sell the repurchased security to get the benefit of a loss deduction.
Cryptocurrency advocates claim that crypto assets are not securities—a position that the chair of the Securities and Exchange Commission has rejected36—and that cryptocurrency transactions are therefore not subject to the wash sale rule. Congress, for its part, has sought to halt the use of cryptocurrency transactions to harvest loss deductions. During consideration of the Build Back Better Act, a much larger bill that was ultimately not enacted, Congress debated language that would clarify that wash sale rules apply to any sale or other disposition of a specified asset, including commodities and “any digital representation of value which is recorded on a cryptographically secured distributed ledger or any similar technology.”37 While further clarification may be needed to specify the details of such a proposal,38 cryptocurrency transactions should be subject to the wash sale rule to prevent tax avoidance.
Close the constructive sales loophole
A related maneuver to avoid tax on capital gain occurs where a taxpayer holding a position in a stock, debt instrument, or partnership where that position has appreciated in value enters into a constructive sale of the appreciated position such that the recognition of gain is deferred and may never occur. To combat this practice, the constructive sales rule39 requires the recognition of taxable gain at fair market value on the date of the constructive sale.40 As recognized by the House and Senate proponents in the same Build Back Better bill cited above,41 digital asset transactions should comply with the constructive sales rule.
Provide clear guidance on hard forks and airdrops
A common cryptocurrency transaction called a “hard fork” occurs when one or more crypto developers modifies the software on which a particular cryptocurrency network, such as Bitcoin, is based, creating two blockchain paths—the old one and the new one. If, at the point of modification (the “fork”), the modified software is fully compatible with the pre-fork version, transactions can continue, in what is known as a “soft fork.” But if the modified software is not compatible, either everyone on the network will be required to shift to the new fork (a noncontentious hard fork) and the old fork will be dismantled, or there is no consensus in the community of the network participants and both forks survive, with different rules for reviewing and verifying transactions (a contentious hard fork).
In October 2019, the IRS issued guidance on the application of the tax law to hard forks.42 However, since then, tax experts have pointed out that the guidance inadvertently caused taxpayer confusion by inaccurately connecting hard forks with another common cryptocurrency transaction: “airdrops.”43 Airdrops are simply gifts of coins or tokens that are distributed to targeted wallets, often as part of a marketing scheme. Importantly, the recipients of an airdrop do not provide consideration for the airdrop and do not have control over whether they receive it. And the recipient may not even have access to the gifted coins or tokens in their wallet until they take specified actions, such as signing up on a website and providing specific information or downloading the new product’s dedicated wallet.44
While hard forks and airdrops often occur simultaneously, they are more appropriately treated as separate transactions. Except in rare instances where a hard fork is actually combined with an airdrop, airdrops are almost always a separate transaction—a gifting transaction—that may or may not occur before, during, or after a hard fork. Indeed, they may occur at any time for any number of reasons.
The IRS should clarify how both contentious and noncontentious hard forks and, separately, airdrops should be treated for federal income tax purposes. For example, noncontentious hard forks need not be treated as taxable events, where the entire network upgrades to the new system and the infrastructure of the old system is dismantled. Importantly, the new coins or tokens should retain the tax basis of the old coins.45 Since the 2019 guidance spoke only to airdrops directly combined with a hard fork—an arrangement that is rare—the IRS should clarify how to treat the more typical airdrops, which, as explained above, are essentially giveaways as part of a marketing scheme.
Modernize rules for loans of cryptocurrency securities
Owners of traditional securities—including pension funds, mutual funds, insurance companies, and other institutional investors—commonly loan securities to others, who compensate them for doing so.46 Under the securities loan nonrecognition rules, when the original owner gets the securities back at the end of the loan agreement, they are not required to recognize gain or loss on the underlying securities if the loan agreement essentially put them in the same economic position they would have been in had they never loaned out the securities. They must receive the same or essentially the same securities in return, and the agreement must require that any payments on the securities during the period of the loan, such as dividends, be paid to the original owner during the course of the loan.
Because the language of the securities loan nonrecognition rules does not expressly include digital assets, nearly all of which are securities, the Biden administration proposed in its fiscal year 2024 budget that actively traded digital assets recorded on cryptographically secured distributed ledgers be included in the definition of “securities” for purposes of the rules.47 This would enable such loans to be tax-free, but only if they are of a reasonable time period and otherwise have standard market terms.
This modernization of the securities loan nonrecognition rules would ensure that loans of digital assets can benefit from the same treatment as other securities but also that they are subject to the same limitations.
See also
Ensure accurate accounting of actively traded digital asset income
Under current law, dealers in securities are required to account for securities they hold at the end of the year as if the securities were sold at fair market value, thereby requiring them to recognize taxable gain or loss.48 Dealers in commodities and traders in securities and commodities may elect to use this method of accounting for their year-end inventories. This can be less burdensome if the dealer already must use the method for financial accounting purposes, and it is accurate for securities that are actively traded.
In its fiscal year 2024 budget, the Biden administration proposed to add actively traded digital assets to the categories of securities that fall under this tax provision to ensure that dealers and brokers using this method of accounting accurately report their gains or losses on digital assets they hold at the end of the year.49 In addition, the Financial Accounting Standards Board, which oversees U.S. Generally Accepted Accounting Principles, recently affirmed the inclusion of certain crypto assets within the scope of its Fair Value Measurement guidance.50
Impose the digital asset mining energy excise tax
The process of mining and managing digital assets is extremely energy intensive. According to a 2022 White House Office of Science and Technology Policy report, crypto assets use between 120 billion and 240 billion kilowatt-hours per year, an amount that exceeds the total annual electricity usage of countries such as Australia or Argentina.51 The same report estimates that crypto-asset operations currently account for 0.9 percent to 1.7 percent of total U.S. electricity usage.
Crypto assets use between 120 billion and 240 billion kilowatt-hours per year, an amount that exceeds the total annual electricity usage of countries such as Australia or Argentina.
Out of concern over climate-related impacts of cryptocurrency operations, as well their implications for stability of the U.S. electricity grid, President Joe Biden’s fiscal year 2024 proposed budget would impose an excise tax equal to 30 percent of the cost of electricity used in cryptocurrency mining on any business using computing resources to mine digital assets, phased in over three years.52 Currently, there are no federal taxes on electricity, nor are there sector-specific energy taxes.53 Energy taxes vary widely among countries; however, the United States ranks among the lowest-taxed countries: 40th out of 44 countries in average effective energy tax rates—mainly due to its fuel excise taxes—according to a recent Organization for Economic Cooperation and Development (OECD) survey of energy tax policies.54
If enacted, the Biden administration proposal would be the first crypto-specific tax. However, concern over the level of energy consumption is not new. Earlier this year, New York state enacted a two-year moratorium within the state on cryptocurrency mining operations powered by carbon-based electricity,55 and the Chinese government has directed electricity providers to stop using the country’s power grid to provide service to crypto miners.56
Congress must be careful not to create new cryptocurrency tax problems
Cryptocurrency advocates continue to push for special tax treatment from Congress and are focusing on specific types of tax benefits to lure more Americans into the cryptocurrency markets and ensure that crypto transactions remain hidden from tax and other regulatory authorities.57 These goals are evident in the provisions of tax proposals already advanced in Congress. In 2022, more than 50 digital asset bills were introduced,58 and several of them proposed changes to the tax treatment of cryptocurrency, mostly in ways that are inconsistent with existing tax law and that could seriously undermine collection of tax revenues. While many of the proposals were not reintroduced in the current Congress, it is worth looking at a few examples of these flawed proposals to ensure they are not advanced.
In 2022, more than 50 digital asset bills were introduced, and several of them proposed changes to the tax treatment of cryptocurrency, mostly in ways that are inconsistent with existing tax law and that could seriously undermine collection of tax revenues.
The risks of providing special tax treatment to cryptocurrencies cannot be understated. Significant revenue loss is sure to follow as taxpayers move assets and transactions into cryptocurrency to take advantage of special rules. Even more concerning, special tax rules for cryptocurrency could exacerbate the already challenging problem of anonymity in crypto transactions, which makes it difficult to determine who owes tax; it could create opportunities for tax evasion, money laundering, terrorist financing, and other illegal activities. The risk is real and, indeed, already happening.
Lessons learned from cryptocurrency scams59 demonstrate why the industry should not be subject to preferential treatment.
Gains from use of cryptocurrency for small purchases should not be excluded from tax
As mentioned above, when an individual uses cryptocurrency to purchase goods or services in the real economy, the tax law treats this as two transactions: a transfer of cryptocurrency property from the original owner to a third party and a purchase of goods and services. As the 2014 IRS guidance made clear,60 when a taxpayer sells or transfers assets they own to another person, they may recognize a gain or loss of income for tax purposes, depending upon the value of what they received in return and their basis in the crypto property. Generally, gains from the transfer of assets held as capital assets for more than a year are considered long-term capital gains, subject to a lower tax rate than short-term gains, which are taxed as ordinary income.61
Several policymakers have proposed excluding these de minimis gains from gross income, on the grounds that they are not worth the administrative burdens of taxing them. The various proposals define small transactions as less than $50,62 $20063, or $600.64 But there is no exclusion for small stock transactions, and there should not be one for cryptocurrency transactions.
Moreover, although the tax benefit per transaction appears small, the cost in terms of lost tax revenue could quickly balloon. While daily Bitcoin transactions dropped significantly after the FTX debacle, they spiked back up in May 2023 and, though lower now, reach more than 4 million per day.65 Also, a number of large companies still accept cryptocurrency payments.66 And even though most of these proposals would not allow a large transaction to be split into smaller transactions to avoid exceeding the reporting threshold, it would be very difficult for the IRS to monitor millions of transactions per day to ensure compliance.
Formalizing special treatment or tax subsidies for cryptocurrency would represent a hand on the scales by tax policymakers—incentivizing greater investment in an unproven and highly volatile type of asset that diverts capital away from much-needed investments in the real economy.
Exclusion of gains on small transactions is a top priority for cryptocurrency advocates, who cannot make profits in the crypto market unless there is significant liquidity—that is, unless a large number of individuals and businesses invest their real money and savings in the market. But there is no reason why gains from cryptocurrency should be treated any differently than those from other assets.
Advocates claim that a small cryptocurrency transaction exclusion would be similar to the current-law exclusion that allows individuals who experience gains from exchanging foreign currency to exclude those gains from gross income for tax purposes.67 But the rationale for the foreign currency exclusion is not at all parallel to U.S. purchases with virtual currencies. A U.S. taxpayer traveling abroad is usually forced to use the local currency, potentially engaging in many transactions per day, with a significant administrative burden to keep track of and report very small gains, or losses, from those daily transactions, while U.S. taxpayers are not forced to use cryptocurrencies for purchases in the United States.68
Mining and staking rewards are ordinary income when received
Consistent with U.S. Supreme Court case law, which holds that any “accession to wealth, clearly realized” must be included in gross income for tax purposes once the taxpayer has complete dominion or control over it,69 cryptocurrency assets received as rewards for validating services are taxable income to the miner or staker at the time they are received.70 The IRS explicitly confirmed this with respect to mining rewards71 and, more recently, with respect to rewards from “staking,”72 a newer form of validation.
The Responsible Financial Innovation Act, introduced by Sens. Cynthia Lummis (R-WY) and Kirsten Gillibrand (D-NY) in the 117th Congress,73 would have allowed miners and stakers to defer taxation of their mining or staking income until they sell or transfer the reward coins or tokens to a third party, which could occur much later or not at all. As experts at the Tax Law Center at New York University Law School have explained, deferring recognition of this otherwise taxable income constitutes a tax subsidy for a special group of taxpayers—miners and stakers of cryptocurrency—with no economic rationale to justify it.74 Rather, it would create a tax incentive for resources “to flow away from other industries and activities towards digital asset mining and staking.”75 Moreover, this unjustified tax preference would lead to lost tax revenue, affecting the federal budget in much the same way as if the federal government “wrote miners and stakers a check.”76
Some cryptocurrency advocates may try to claim that tax breaks for miners and stakers will promote innovation in crypto markets. But deferral of income recognition could actually stifle innovation, as it creates an incentive to hold onto assets rather than use them for new transactions, in what is known as the lock-in effect.77 Allowing deferral of income recognition for special groups of taxpayers, especially without a strong economic justification, is unfair to others who pay tax on their ordinary income at the time they receive it.
Decentralized autonomous organizations and decentralized finance should be taxed
Decentralized autonomous organizations (DAOs) are a type of decentralized finance (DeFi), which refers to peer-to-peer financial transactions enabled by a computer protocol, rather than by traditional intermediaries such as banks, brokers, custodians, and clearing house firms.78 DAOs are essentially groups of investors, and when not otherwise incorporated, they claim that they are not taxable as entities because there is no centralized taxable entity.79 However, DAOs do have centralized managers or a handful of token holders that have most of the voting power.80
Allowing DAOs to go untaxed at the entity level would facilitate huge opportunities for tax avoidance, especially as these structures become increasingly adept at masking the identity of their owners. In addition to tax avoidance, these organizations raise serious national security concerns, which Sen. Elizabeth Warren (D-MA) has highlighted in public statements81 and sought to address through legislation.82 It would be advisable for Congress to get out ahead of the tax and other issues raised by DAOs before these arrangements cause significant harm to U.S. revenue and national security interests.
Related read
Conclusion
Events over the past year and a half have focused scrutiny on the outlandish claims of the cryptocurrency industry and how it should be regulated. Much of this turmoil could have been avoided if the industry had been more consistently subjected to long-standing regulatory structures designed to protect consumers and the stability of financial markets. Similarly, the industry’s attempt to exclude itself from established tax laws has fueled a widening tax gap.
Formalizing special treatment or tax subsidies for cryptocurrency would represent a hand on the scales by tax policymakers—incentivizing greater investment in an unproven and highly volatile type of asset that diverts capital away from much-needed investments in the real economy. Even worse, policymakers could inadvertently increase the rewards and hence the attraction of cryptocurrencies as a tool used by nefarious actors seeking to launder ill-gotten gains, skirt international sanctions, or finance terrorism.
The Treasury Department and the IRS should act swiftly to issue guidance where it is needed to clarify the application of existing laws governing income recognition and reporting to the cryptocurrency industry and cryptocurrency transactions. Absent broad-based agreement on the need for legislative language, Congress should allow the Treasury and IRS to move forward with educating taxpayers and enforcing the tax laws.
Acknowledgments
The authors would like to thank Mark Hays and Taylor Cranor for their comments on an earlier draft. Any mistakes are the authors’ own.